num_traits/
cast.rs

1use core::mem::size_of;
2use core::num::Wrapping;
3use core::{f32, f64};
4#[cfg(has_i128)]
5use core::{i128, u128};
6use core::{i16, i32, i64, i8, isize};
7use core::{u16, u32, u64, u8, usize};
8
9/// A generic trait for converting a value to a number.
10///
11/// A value can be represented by the target type when it lies within
12/// the range of scalars supported by the target type.
13/// For example, a negative integer cannot be represented by an unsigned
14/// integer type, and an `i64` with a very high magnitude might not be
15/// convertible to an `i32`.
16/// On the other hand, conversions with possible precision loss or truncation
17/// are admitted, like an `f32` with a decimal part to an integer type, or
18/// even a large `f64` saturating to `f32` infinity.
19pub trait ToPrimitive {
20    /// Converts the value of `self` to an `isize`. If the value cannot be
21    /// represented by an `isize`, then `None` is returned.
22    #[inline]
23    fn to_isize(&self) -> Option<isize> {
24        self.to_i64().as_ref().and_then(ToPrimitive::to_isize)
25    }
26
27    /// Converts the value of `self` to an `i8`. If the value cannot be
28    /// represented by an `i8`, then `None` is returned.
29    #[inline]
30    fn to_i8(&self) -> Option<i8> {
31        self.to_i64().as_ref().and_then(ToPrimitive::to_i8)
32    }
33
34    /// Converts the value of `self` to an `i16`. If the value cannot be
35    /// represented by an `i16`, then `None` is returned.
36    #[inline]
37    fn to_i16(&self) -> Option<i16> {
38        self.to_i64().as_ref().and_then(ToPrimitive::to_i16)
39    }
40
41    /// Converts the value of `self` to an `i32`. If the value cannot be
42    /// represented by an `i32`, then `None` is returned.
43    #[inline]
44    fn to_i32(&self) -> Option<i32> {
45        self.to_i64().as_ref().and_then(ToPrimitive::to_i32)
46    }
47
48    /// Converts the value of `self` to an `i64`. If the value cannot be
49    /// represented by an `i64`, then `None` is returned.
50    fn to_i64(&self) -> Option<i64>;
51
52    /// Converts the value of `self` to an `i128`. If the value cannot be
53    /// represented by an `i128` (`i64` under the default implementation), then
54    /// `None` is returned.
55    ///
56    /// This method is only available with feature `i128` enabled on Rust >= 1.26.
57    ///
58    /// The default implementation converts through `to_i64()`. Types implementing
59    /// this trait should override this method if they can represent a greater range.
60    #[inline]
61    #[cfg(has_i128)]
62    fn to_i128(&self) -> Option<i128> {
63        self.to_i64().map(From::from)
64    }
65
66    /// Converts the value of `self` to a `usize`. If the value cannot be
67    /// represented by a `usize`, then `None` is returned.
68    #[inline]
69    fn to_usize(&self) -> Option<usize> {
70        self.to_u64().as_ref().and_then(ToPrimitive::to_usize)
71    }
72
73    /// Converts the value of `self` to a `u8`. If the value cannot be
74    /// represented by a `u8`, then `None` is returned.
75    #[inline]
76    fn to_u8(&self) -> Option<u8> {
77        self.to_u64().as_ref().and_then(ToPrimitive::to_u8)
78    }
79
80    /// Converts the value of `self` to a `u16`. If the value cannot be
81    /// represented by a `u16`, then `None` is returned.
82    #[inline]
83    fn to_u16(&self) -> Option<u16> {
84        self.to_u64().as_ref().and_then(ToPrimitive::to_u16)
85    }
86
87    /// Converts the value of `self` to a `u32`. If the value cannot be
88    /// represented by a `u32`, then `None` is returned.
89    #[inline]
90    fn to_u32(&self) -> Option<u32> {
91        self.to_u64().as_ref().and_then(ToPrimitive::to_u32)
92    }
93
94    /// Converts the value of `self` to a `u64`. If the value cannot be
95    /// represented by a `u64`, then `None` is returned.
96    fn to_u64(&self) -> Option<u64>;
97
98    /// Converts the value of `self` to a `u128`. If the value cannot be
99    /// represented by a `u128` (`u64` under the default implementation), then
100    /// `None` is returned.
101    ///
102    /// This method is only available with feature `i128` enabled on Rust >= 1.26.
103    ///
104    /// The default implementation converts through `to_u64()`. Types implementing
105    /// this trait should override this method if they can represent a greater range.
106    #[inline]
107    #[cfg(has_i128)]
108    fn to_u128(&self) -> Option<u128> {
109        self.to_u64().map(From::from)
110    }
111
112    /// Converts the value of `self` to an `f32`. Overflows may map to positive
113    /// or negative inifinity, otherwise `None` is returned if the value cannot
114    /// be represented by an `f32`.
115    #[inline]
116    fn to_f32(&self) -> Option<f32> {
117        self.to_f64().as_ref().and_then(ToPrimitive::to_f32)
118    }
119
120    /// Converts the value of `self` to an `f64`. Overflows may map to positive
121    /// or negative inifinity, otherwise `None` is returned if the value cannot
122    /// be represented by an `f64`.
123    ///
124    /// The default implementation tries to convert through `to_i64()`, and
125    /// failing that through `to_u64()`. Types implementing this trait should
126    /// override this method if they can represent a greater range.
127    #[inline]
128    fn to_f64(&self) -> Option<f64> {
129        match self.to_i64() {
130            Some(i) => i.to_f64(),
131            None => self.to_u64().as_ref().and_then(ToPrimitive::to_f64),
132        }
133    }
134}
135
136macro_rules! impl_to_primitive_int_to_int {
137    ($SrcT:ident : $( $(#[$cfg:meta])* fn $method:ident -> $DstT:ident ; )*) => {$(
138        #[inline]
139        $(#[$cfg])*
140        fn $method(&self) -> Option<$DstT> {
141            let min = $DstT::MIN as $SrcT;
142            let max = $DstT::MAX as $SrcT;
143            if size_of::<$SrcT>() <= size_of::<$DstT>() || (min <= *self && *self <= max) {
144                Some(*self as $DstT)
145            } else {
146                None
147            }
148        }
149    )*}
150}
151
152macro_rules! impl_to_primitive_int_to_uint {
153    ($SrcT:ident : $( $(#[$cfg:meta])* fn $method:ident -> $DstT:ident ; )*) => {$(
154        #[inline]
155        $(#[$cfg])*
156        fn $method(&self) -> Option<$DstT> {
157            let max = $DstT::MAX as $SrcT;
158            if 0 <= *self && (size_of::<$SrcT>() <= size_of::<$DstT>() || *self <= max) {
159                Some(*self as $DstT)
160            } else {
161                None
162            }
163        }
164    )*}
165}
166
167macro_rules! impl_to_primitive_int {
168    ($T:ident) => {
169        impl ToPrimitive for $T {
170            impl_to_primitive_int_to_int! { $T:
171                fn to_isize -> isize;
172                fn to_i8 -> i8;
173                fn to_i16 -> i16;
174                fn to_i32 -> i32;
175                fn to_i64 -> i64;
176                #[cfg(has_i128)]
177                fn to_i128 -> i128;
178            }
179
180            impl_to_primitive_int_to_uint! { $T:
181                fn to_usize -> usize;
182                fn to_u8 -> u8;
183                fn to_u16 -> u16;
184                fn to_u32 -> u32;
185                fn to_u64 -> u64;
186                #[cfg(has_i128)]
187                fn to_u128 -> u128;
188            }
189
190            #[inline]
191            fn to_f32(&self) -> Option<f32> {
192                Some(*self as f32)
193            }
194            #[inline]
195            fn to_f64(&self) -> Option<f64> {
196                Some(*self as f64)
197            }
198        }
199    };
200}
201
202impl_to_primitive_int!(isize);
203impl_to_primitive_int!(i8);
204impl_to_primitive_int!(i16);
205impl_to_primitive_int!(i32);
206impl_to_primitive_int!(i64);
207#[cfg(has_i128)]
208impl_to_primitive_int!(i128);
209
210macro_rules! impl_to_primitive_uint_to_int {
211    ($SrcT:ident : $( $(#[$cfg:meta])* fn $method:ident -> $DstT:ident ; )*) => {$(
212        #[inline]
213        $(#[$cfg])*
214        fn $method(&self) -> Option<$DstT> {
215            let max = $DstT::MAX as $SrcT;
216            if size_of::<$SrcT>() < size_of::<$DstT>() || *self <= max {
217                Some(*self as $DstT)
218            } else {
219                None
220            }
221        }
222    )*}
223}
224
225macro_rules! impl_to_primitive_uint_to_uint {
226    ($SrcT:ident : $( $(#[$cfg:meta])* fn $method:ident -> $DstT:ident ; )*) => {$(
227        #[inline]
228        $(#[$cfg])*
229        fn $method(&self) -> Option<$DstT> {
230            let max = $DstT::MAX as $SrcT;
231            if size_of::<$SrcT>() <= size_of::<$DstT>() || *self <= max {
232                Some(*self as $DstT)
233            } else {
234                None
235            }
236        }
237    )*}
238}
239
240macro_rules! impl_to_primitive_uint {
241    ($T:ident) => {
242        impl ToPrimitive for $T {
243            impl_to_primitive_uint_to_int! { $T:
244                fn to_isize -> isize;
245                fn to_i8 -> i8;
246                fn to_i16 -> i16;
247                fn to_i32 -> i32;
248                fn to_i64 -> i64;
249                #[cfg(has_i128)]
250                fn to_i128 -> i128;
251            }
252
253            impl_to_primitive_uint_to_uint! { $T:
254                fn to_usize -> usize;
255                fn to_u8 -> u8;
256                fn to_u16 -> u16;
257                fn to_u32 -> u32;
258                fn to_u64 -> u64;
259                #[cfg(has_i128)]
260                fn to_u128 -> u128;
261            }
262
263            #[inline]
264            fn to_f32(&self) -> Option<f32> {
265                Some(*self as f32)
266            }
267            #[inline]
268            fn to_f64(&self) -> Option<f64> {
269                Some(*self as f64)
270            }
271        }
272    };
273}
274
275impl_to_primitive_uint!(usize);
276impl_to_primitive_uint!(u8);
277impl_to_primitive_uint!(u16);
278impl_to_primitive_uint!(u32);
279impl_to_primitive_uint!(u64);
280#[cfg(has_i128)]
281impl_to_primitive_uint!(u128);
282
283macro_rules! impl_to_primitive_float_to_float {
284    ($SrcT:ident : $( fn $method:ident -> $DstT:ident ; )*) => {$(
285        #[inline]
286        fn $method(&self) -> Option<$DstT> {
287            // We can safely cast all values, whether NaN, +-inf, or finite.
288            // Finite values that are reducing size may saturate to +-inf.
289            Some(*self as $DstT)
290        }
291    )*}
292}
293
294#[cfg(has_to_int_unchecked)]
295macro_rules! float_to_int_unchecked {
296    // SAFETY: Must not be NaN or infinite; must be representable as the integer after truncating.
297    // We already checked that the float is in the exclusive range `(MIN-1, MAX+1)`.
298    ($float:expr => $int:ty) => {
299        unsafe { $float.to_int_unchecked::<$int>() }
300    };
301}
302
303#[cfg(not(has_to_int_unchecked))]
304macro_rules! float_to_int_unchecked {
305    ($float:expr => $int:ty) => {
306        $float as $int
307    };
308}
309
310macro_rules! impl_to_primitive_float_to_signed_int {
311    ($f:ident : $( $(#[$cfg:meta])* fn $method:ident -> $i:ident ; )*) => {$(
312        #[inline]
313        $(#[$cfg])*
314        fn $method(&self) -> Option<$i> {
315            // Float as int truncates toward zero, so we want to allow values
316            // in the exclusive range `(MIN-1, MAX+1)`.
317            if size_of::<$f>() > size_of::<$i>() {
318                // With a larger size, we can represent the range exactly.
319                const MIN_M1: $f = $i::MIN as $f - 1.0;
320                const MAX_P1: $f = $i::MAX as $f + 1.0;
321                if *self > MIN_M1 && *self < MAX_P1 {
322                    return Some(float_to_int_unchecked!(*self => $i));
323                }
324            } else {
325                // We can't represent `MIN-1` exactly, but there's no fractional part
326                // at this magnitude, so we can just use a `MIN` inclusive boundary.
327                const MIN: $f = $i::MIN as $f;
328                // We can't represent `MAX` exactly, but it will round up to exactly
329                // `MAX+1` (a power of two) when we cast it.
330                const MAX_P1: $f = $i::MAX as $f;
331                if *self >= MIN && *self < MAX_P1 {
332                    return Some(float_to_int_unchecked!(*self => $i));
333                }
334            }
335            None
336        }
337    )*}
338}
339
340macro_rules! impl_to_primitive_float_to_unsigned_int {
341    ($f:ident : $( $(#[$cfg:meta])* fn $method:ident -> $u:ident ; )*) => {$(
342        #[inline]
343        $(#[$cfg])*
344        fn $method(&self) -> Option<$u> {
345            // Float as int truncates toward zero, so we want to allow values
346            // in the exclusive range `(-1, MAX+1)`.
347            if size_of::<$f>() > size_of::<$u>() {
348                // With a larger size, we can represent the range exactly.
349                const MAX_P1: $f = $u::MAX as $f + 1.0;
350                if *self > -1.0 && *self < MAX_P1 {
351                    return Some(float_to_int_unchecked!(*self => $u));
352                }
353            } else {
354                // We can't represent `MAX` exactly, but it will round up to exactly
355                // `MAX+1` (a power of two) when we cast it.
356                // (`u128::MAX as f32` is infinity, but this is still ok.)
357                const MAX_P1: $f = $u::MAX as $f;
358                if *self > -1.0 && *self < MAX_P1 {
359                    return Some(float_to_int_unchecked!(*self => $u));
360                }
361            }
362            None
363        }
364    )*}
365}
366
367macro_rules! impl_to_primitive_float {
368    ($T:ident) => {
369        impl ToPrimitive for $T {
370            impl_to_primitive_float_to_signed_int! { $T:
371                fn to_isize -> isize;
372                fn to_i8 -> i8;
373                fn to_i16 -> i16;
374                fn to_i32 -> i32;
375                fn to_i64 -> i64;
376                #[cfg(has_i128)]
377                fn to_i128 -> i128;
378            }
379
380            impl_to_primitive_float_to_unsigned_int! { $T:
381                fn to_usize -> usize;
382                fn to_u8 -> u8;
383                fn to_u16 -> u16;
384                fn to_u32 -> u32;
385                fn to_u64 -> u64;
386                #[cfg(has_i128)]
387                fn to_u128 -> u128;
388            }
389
390            impl_to_primitive_float_to_float! { $T:
391                fn to_f32 -> f32;
392                fn to_f64 -> f64;
393            }
394        }
395    };
396}
397
398impl_to_primitive_float!(f32);
399impl_to_primitive_float!(f64);
400
401/// A generic trait for converting a number to a value.
402///
403/// A value can be represented by the target type when it lies within
404/// the range of scalars supported by the target type.
405/// For example, a negative integer cannot be represented by an unsigned
406/// integer type, and an `i64` with a very high magnitude might not be
407/// convertible to an `i32`.
408/// On the other hand, conversions with possible precision loss or truncation
409/// are admitted, like an `f32` with a decimal part to an integer type, or
410/// even a large `f64` saturating to `f32` infinity.
411pub trait FromPrimitive: Sized {
412    /// Converts an `isize` to return an optional value of this type. If the
413    /// value cannot be represented by this type, then `None` is returned.
414    #[inline]
415    fn from_isize(n: isize) -> Option<Self> {
416        n.to_i64().and_then(FromPrimitive::from_i64)
417    }
418
419    /// Converts an `i8` to return an optional value of this type. If the
420    /// value cannot be represented by this type, then `None` is returned.
421    #[inline]
422    fn from_i8(n: i8) -> Option<Self> {
423        FromPrimitive::from_i64(From::from(n))
424    }
425
426    /// Converts an `i16` to return an optional value of this type. If the
427    /// value cannot be represented by this type, then `None` is returned.
428    #[inline]
429    fn from_i16(n: i16) -> Option<Self> {
430        FromPrimitive::from_i64(From::from(n))
431    }
432
433    /// Converts an `i32` to return an optional value of this type. If the
434    /// value cannot be represented by this type, then `None` is returned.
435    #[inline]
436    fn from_i32(n: i32) -> Option<Self> {
437        FromPrimitive::from_i64(From::from(n))
438    }
439
440    /// Converts an `i64` to return an optional value of this type. If the
441    /// value cannot be represented by this type, then `None` is returned.
442    fn from_i64(n: i64) -> Option<Self>;
443
444    /// Converts an `i128` to return an optional value of this type. If the
445    /// value cannot be represented by this type, then `None` is returned.
446    ///
447    /// This method is only available with feature `i128` enabled on Rust >= 1.26.
448    ///
449    /// The default implementation converts through `from_i64()`. Types implementing
450    /// this trait should override this method if they can represent a greater range.
451    #[inline]
452    #[cfg(has_i128)]
453    fn from_i128(n: i128) -> Option<Self> {
454        n.to_i64().and_then(FromPrimitive::from_i64)
455    }
456
457    /// Converts a `usize` to return an optional value of this type. If the
458    /// value cannot be represented by this type, then `None` is returned.
459    #[inline]
460    fn from_usize(n: usize) -> Option<Self> {
461        n.to_u64().and_then(FromPrimitive::from_u64)
462    }
463
464    /// Converts an `u8` to return an optional value of this type. If the
465    /// value cannot be represented by this type, then `None` is returned.
466    #[inline]
467    fn from_u8(n: u8) -> Option<Self> {
468        FromPrimitive::from_u64(From::from(n))
469    }
470
471    /// Converts an `u16` to return an optional value of this type. If the
472    /// value cannot be represented by this type, then `None` is returned.
473    #[inline]
474    fn from_u16(n: u16) -> Option<Self> {
475        FromPrimitive::from_u64(From::from(n))
476    }
477
478    /// Converts an `u32` to return an optional value of this type. If the
479    /// value cannot be represented by this type, then `None` is returned.
480    #[inline]
481    fn from_u32(n: u32) -> Option<Self> {
482        FromPrimitive::from_u64(From::from(n))
483    }
484
485    /// Converts an `u64` to return an optional value of this type. If the
486    /// value cannot be represented by this type, then `None` is returned.
487    fn from_u64(n: u64) -> Option<Self>;
488
489    /// Converts an `u128` to return an optional value of this type. If the
490    /// value cannot be represented by this type, then `None` is returned.
491    ///
492    /// This method is only available with feature `i128` enabled on Rust >= 1.26.
493    ///
494    /// The default implementation converts through `from_u64()`. Types implementing
495    /// this trait should override this method if they can represent a greater range.
496    #[inline]
497    #[cfg(has_i128)]
498    fn from_u128(n: u128) -> Option<Self> {
499        n.to_u64().and_then(FromPrimitive::from_u64)
500    }
501
502    /// Converts a `f32` to return an optional value of this type. If the
503    /// value cannot be represented by this type, then `None` is returned.
504    #[inline]
505    fn from_f32(n: f32) -> Option<Self> {
506        FromPrimitive::from_f64(From::from(n))
507    }
508
509    /// Converts a `f64` to return an optional value of this type. If the
510    /// value cannot be represented by this type, then `None` is returned.
511    ///
512    /// The default implementation tries to convert through `from_i64()`, and
513    /// failing that through `from_u64()`. Types implementing this trait should
514    /// override this method if they can represent a greater range.
515    #[inline]
516    fn from_f64(n: f64) -> Option<Self> {
517        match n.to_i64() {
518            Some(i) => FromPrimitive::from_i64(i),
519            None => n.to_u64().and_then(FromPrimitive::from_u64),
520        }
521    }
522}
523
524macro_rules! impl_from_primitive {
525    ($T:ty, $to_ty:ident) => {
526        #[allow(deprecated)]
527        impl FromPrimitive for $T {
528            #[inline]
529            fn from_isize(n: isize) -> Option<$T> {
530                n.$to_ty()
531            }
532            #[inline]
533            fn from_i8(n: i8) -> Option<$T> {
534                n.$to_ty()
535            }
536            #[inline]
537            fn from_i16(n: i16) -> Option<$T> {
538                n.$to_ty()
539            }
540            #[inline]
541            fn from_i32(n: i32) -> Option<$T> {
542                n.$to_ty()
543            }
544            #[inline]
545            fn from_i64(n: i64) -> Option<$T> {
546                n.$to_ty()
547            }
548            #[cfg(has_i128)]
549            #[inline]
550            fn from_i128(n: i128) -> Option<$T> {
551                n.$to_ty()
552            }
553
554            #[inline]
555            fn from_usize(n: usize) -> Option<$T> {
556                n.$to_ty()
557            }
558            #[inline]
559            fn from_u8(n: u8) -> Option<$T> {
560                n.$to_ty()
561            }
562            #[inline]
563            fn from_u16(n: u16) -> Option<$T> {
564                n.$to_ty()
565            }
566            #[inline]
567            fn from_u32(n: u32) -> Option<$T> {
568                n.$to_ty()
569            }
570            #[inline]
571            fn from_u64(n: u64) -> Option<$T> {
572                n.$to_ty()
573            }
574            #[cfg(has_i128)]
575            #[inline]
576            fn from_u128(n: u128) -> Option<$T> {
577                n.$to_ty()
578            }
579
580            #[inline]
581            fn from_f32(n: f32) -> Option<$T> {
582                n.$to_ty()
583            }
584            #[inline]
585            fn from_f64(n: f64) -> Option<$T> {
586                n.$to_ty()
587            }
588        }
589    };
590}
591
592impl_from_primitive!(isize, to_isize);
593impl_from_primitive!(i8, to_i8);
594impl_from_primitive!(i16, to_i16);
595impl_from_primitive!(i32, to_i32);
596impl_from_primitive!(i64, to_i64);
597#[cfg(has_i128)]
598impl_from_primitive!(i128, to_i128);
599impl_from_primitive!(usize, to_usize);
600impl_from_primitive!(u8, to_u8);
601impl_from_primitive!(u16, to_u16);
602impl_from_primitive!(u32, to_u32);
603impl_from_primitive!(u64, to_u64);
604#[cfg(has_i128)]
605impl_from_primitive!(u128, to_u128);
606impl_from_primitive!(f32, to_f32);
607impl_from_primitive!(f64, to_f64);
608
609macro_rules! impl_to_primitive_wrapping {
610    ($( $(#[$cfg:meta])* fn $method:ident -> $i:ident ; )*) => {$(
611        #[inline]
612        $(#[$cfg])*
613        fn $method(&self) -> Option<$i> {
614            (self.0).$method()
615        }
616    )*}
617}
618
619impl<T: ToPrimitive> ToPrimitive for Wrapping<T> {
620    impl_to_primitive_wrapping! {
621        fn to_isize -> isize;
622        fn to_i8 -> i8;
623        fn to_i16 -> i16;
624        fn to_i32 -> i32;
625        fn to_i64 -> i64;
626        #[cfg(has_i128)]
627        fn to_i128 -> i128;
628
629        fn to_usize -> usize;
630        fn to_u8 -> u8;
631        fn to_u16 -> u16;
632        fn to_u32 -> u32;
633        fn to_u64 -> u64;
634        #[cfg(has_i128)]
635        fn to_u128 -> u128;
636
637        fn to_f32 -> f32;
638        fn to_f64 -> f64;
639    }
640}
641
642macro_rules! impl_from_primitive_wrapping {
643    ($( $(#[$cfg:meta])* fn $method:ident ( $i:ident ); )*) => {$(
644        #[inline]
645        $(#[$cfg])*
646        fn $method(n: $i) -> Option<Self> {
647            T::$method(n).map(Wrapping)
648        }
649    )*}
650}
651
652impl<T: FromPrimitive> FromPrimitive for Wrapping<T> {
653    impl_from_primitive_wrapping! {
654        fn from_isize(isize);
655        fn from_i8(i8);
656        fn from_i16(i16);
657        fn from_i32(i32);
658        fn from_i64(i64);
659        #[cfg(has_i128)]
660        fn from_i128(i128);
661
662        fn from_usize(usize);
663        fn from_u8(u8);
664        fn from_u16(u16);
665        fn from_u32(u32);
666        fn from_u64(u64);
667        #[cfg(has_i128)]
668        fn from_u128(u128);
669
670        fn from_f32(f32);
671        fn from_f64(f64);
672    }
673}
674
675/// Cast from one machine scalar to another.
676///
677/// # Examples
678///
679/// ```
680/// # use num_traits as num;
681/// let twenty: f32 = num::cast(0x14).unwrap();
682/// assert_eq!(twenty, 20f32);
683/// ```
684///
685#[inline]
686pub fn cast<T: NumCast, U: NumCast>(n: T) -> Option<U> {
687    NumCast::from(n)
688}
689
690/// An interface for casting between machine scalars.
691pub trait NumCast: Sized + ToPrimitive {
692    /// Creates a number from another value that can be converted into
693    /// a primitive via the `ToPrimitive` trait. If the source value cannot be
694    /// represented by the target type, then `None` is returned.
695    ///
696    /// A value can be represented by the target type when it lies within
697    /// the range of scalars supported by the target type.
698    /// For example, a negative integer cannot be represented by an unsigned
699    /// integer type, and an `i64` with a very high magnitude might not be
700    /// convertible to an `i32`.
701    /// On the other hand, conversions with possible precision loss or truncation
702    /// are admitted, like an `f32` with a decimal part to an integer type, or
703    /// even a large `f64` saturating to `f32` infinity.
704    fn from<T: ToPrimitive>(n: T) -> Option<Self>;
705}
706
707macro_rules! impl_num_cast {
708    ($T:ty, $conv:ident) => {
709        impl NumCast for $T {
710            #[inline]
711            #[allow(deprecated)]
712            fn from<N: ToPrimitive>(n: N) -> Option<$T> {
713                // `$conv` could be generated using `concat_idents!`, but that
714                // macro seems to be broken at the moment
715                n.$conv()
716            }
717        }
718    };
719}
720
721impl_num_cast!(u8, to_u8);
722impl_num_cast!(u16, to_u16);
723impl_num_cast!(u32, to_u32);
724impl_num_cast!(u64, to_u64);
725#[cfg(has_i128)]
726impl_num_cast!(u128, to_u128);
727impl_num_cast!(usize, to_usize);
728impl_num_cast!(i8, to_i8);
729impl_num_cast!(i16, to_i16);
730impl_num_cast!(i32, to_i32);
731impl_num_cast!(i64, to_i64);
732#[cfg(has_i128)]
733impl_num_cast!(i128, to_i128);
734impl_num_cast!(isize, to_isize);
735impl_num_cast!(f32, to_f32);
736impl_num_cast!(f64, to_f64);
737
738impl<T: NumCast> NumCast for Wrapping<T> {
739    fn from<U: ToPrimitive>(n: U) -> Option<Self> {
740        T::from(n).map(Wrapping)
741    }
742}
743
744/// A generic interface for casting between machine scalars with the
745/// `as` operator, which admits narrowing and precision loss.
746/// Implementers of this trait `AsPrimitive` should behave like a primitive
747/// numeric type (e.g. a newtype around another primitive), and the
748/// intended conversion must never fail.
749///
750/// # Examples
751///
752/// ```
753/// # use num_traits::AsPrimitive;
754/// let three: i32 = (3.14159265f32).as_();
755/// assert_eq!(three, 3);
756/// ```
757///
758/// # Safety
759///
760/// **In Rust versions before 1.45.0**, some uses of the `as` operator were not entirely safe.
761/// In particular, it was undefined behavior if
762/// a truncated floating point value could not fit in the target integer
763/// type ([#10184](https://github.com/rust-lang/rust/issues/10184)).
764///
765/// ```ignore
766/// # use num_traits::AsPrimitive;
767/// let x: u8 = (1.04E+17).as_(); // UB
768/// ```
769///
770pub trait AsPrimitive<T>: 'static + Copy
771where
772    T: 'static + Copy,
773{
774    /// Convert a value to another, using the `as` operator.
775    fn as_(self) -> T;
776}
777
778macro_rules! impl_as_primitive {
779    (@ $T: ty => $(#[$cfg:meta])* impl $U: ty ) => {
780        $(#[$cfg])*
781        impl AsPrimitive<$U> for $T {
782            #[inline] fn as_(self) -> $U { self as $U }
783        }
784    };
785    (@ $T: ty => { $( $U: ty ),* } ) => {$(
786        impl_as_primitive!(@ $T => impl $U);
787    )*};
788    ($T: ty => { $( $U: ty ),* } ) => {
789        impl_as_primitive!(@ $T => { $( $U ),* });
790        impl_as_primitive!(@ $T => { u8, u16, u32, u64, usize });
791        impl_as_primitive!(@ $T => #[cfg(has_i128)] impl u128);
792        impl_as_primitive!(@ $T => { i8, i16, i32, i64, isize });
793        impl_as_primitive!(@ $T => #[cfg(has_i128)] impl i128);
794    };
795}
796
797impl_as_primitive!(u8 => { char, f32, f64 });
798impl_as_primitive!(i8 => { f32, f64 });
799impl_as_primitive!(u16 => { f32, f64 });
800impl_as_primitive!(i16 => { f32, f64 });
801impl_as_primitive!(u32 => { f32, f64 });
802impl_as_primitive!(i32 => { f32, f64 });
803impl_as_primitive!(u64 => { f32, f64 });
804impl_as_primitive!(i64 => { f32, f64 });
805#[cfg(has_i128)]
806impl_as_primitive!(u128 => { f32, f64 });
807#[cfg(has_i128)]
808impl_as_primitive!(i128 => { f32, f64 });
809impl_as_primitive!(usize => { f32, f64 });
810impl_as_primitive!(isize => { f32, f64 });
811impl_as_primitive!(f32 => { f32, f64 });
812impl_as_primitive!(f64 => { f32, f64 });
813impl_as_primitive!(char => { char });
814impl_as_primitive!(bool => {});
num_traits/cast.rs

num_traits/
cast.rs
