Created
August 11, 2017 14:44
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string と char[] の FieldOffset を重ねてしまう
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using System; | |
using System.Runtime.InteropServices; | |
// | |
[StructLayout(LayoutKind.Explicit)] | |
struct StringOrCharArray | |
{ | |
[FieldOffset(0)] | |
private StringSegment _string; | |
// ArraySegment の private field の並びが 配列, int, int になっているという前提。 | |
// 一応 Mono と CoreCLR ではこの並びになってるけども、割かし危険な類の前提なのでやるかどうか悩むところ | |
[FieldOffset(0)] | |
private ArraySegment<char> _array; | |
// is string 判定用に、StringSegment._string と ArraySegment<T>._array の位置に重ねて object 型のフィールドを定義 | |
[FieldOffset(0)] | |
private object _obj; | |
public StringOrCharArray(string s) : this() => _string = new StringSegment(s, 0, s.Length); | |
public StringOrCharArray(string s, int offset, int count) : this() => _string = new StringSegment(s, offset, count); | |
public StringOrCharArray(char[] s) : this() => _array = new ArraySegment<char>(s, 0, s.Length); | |
public StringOrCharArray(char[] s, int offset, int count) : this() => _array = new ArraySegment<char>(s, offset, count); | |
private bool IsString => _obj is string; | |
// 動作確認用なので、とりあえず ToString だけ実装 | |
public override string ToString() => IsString ? _string.ToString() : new string(_array.Array, _array.Offset, _array.Count); | |
} | |
struct StringSegment | |
{ | |
string _string; | |
int _offset; | |
int _count; | |
public StringSegment(string s, int offeset, int count) | |
{ | |
_string = s; | |
_offset = offeset; | |
_count = count; | |
} | |
public override string ToString() => _string.Substring(_offset, _count); | |
} | |
class Program | |
{ | |
static void Main() | |
{ | |
Console.WriteLine(new StringOrCharArray("abcdefg")); | |
Console.WriteLine(new StringOrCharArray("abcdefg", 2, 3)); | |
Console.WriteLine(new StringOrCharArray(new[] { 'a', 'b', 'c', 'd', 'e', 'f', 'g' })); | |
Console.WriteLine(new StringOrCharArray(new[] { 'a', 'b', 'c', 'd', 'e', 'f', 'g' }, 2, 3)); | |
// string, int, int もしくは char[], int, int を完全に重ねてあるので、構造体サイズが16 | |
Console.WriteLine(System.Runtime.CompilerServices.Unsafe.SizeOf<StringOrCharArray>()); | |
} | |
} |
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