issue47716.go

     1  // run
     2  
     3  // Copyright 2021 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package main
     8  
     9  import (
    10  	"fmt"
    11  	"unsafe"
    12  )
    13  
    14  // size returns the size of type T
    15  func size[T any](x T) uintptr {
    16  	return unsafe.Sizeof(x)
    17  }
    18  
    19  // size returns the alignment of type T
    20  func align[T any](x T) uintptr {
    21  	return unsafe.Alignof(x)
    22  }
    23  
    24  type Tstruct[T any] struct {
    25  	f1 T
    26  	f2 int
    27  }
    28  
    29  // offset returns the offset of field f2 in the generic type Tstruct
    30  func (r *Tstruct[T]) offset() uintptr {
    31  	return unsafe.Offsetof(r.f2)
    32  }
    33  
    34  func main() {
    35  	v1 := int(5)
    36  	if got, want := size(v1), unsafe.Sizeof(v1); got != want {
    37  		panic(fmt.Sprintf("got %d, want %d", got, want))
    38  	}
    39  	if got, want := align(v1), unsafe.Alignof(v1); got != want {
    40  		panic(fmt.Sprintf("got %d, want %d", got, want))
    41  	}
    42  
    43  	v2 := "abc"
    44  	if got, want := size(v2), unsafe.Sizeof(v2); got != want {
    45  		panic(fmt.Sprintf("got %d, want %d", got, want))
    46  	}
    47  	if got, want := align(v2), unsafe.Alignof(v2); got != want {
    48  		panic(fmt.Sprintf("got %d, want %d", got, want))
    49  	}
    50  
    51  	var v3 Tstruct[int]
    52  	if got, want := unsafe.Offsetof(v3.f2), unsafe.Sizeof(v1); got != want {
    53  		panic(fmt.Sprintf("got %d, want %d", got, want))
    54  	}
    55  
    56  	var v4 Tstruct[interface{}]
    57  	var v5 interface{}
    58  	if got, want := unsafe.Offsetof(v4.f2), unsafe.Sizeof(v5); got != want {
    59  		panic(fmt.Sprintf("got %d, want %d", got, want))
    60  	}
    61  
    62  	if got, want := v3.offset(), unsafe.Offsetof(v3.f2); got != want {
    63  		panic(fmt.Sprintf("got %d, want %d", got, want))
    64  	}
    65  	if got, want := v4.offset(), unsafe.Offsetof(v4.f2); got != want {
    66  		panic(fmt.Sprintf("got %d, want %d", got, want))
    67  	}
    68  }
    69
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