delphi 数组竟然可以这样定义


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 数组竟然可以这样定义
//这是常规思路:
const
arr: array[0..1] of Char = ('A','B');
begin
ShowMessage(arr); {AB}
ShowMessage(IntToStr(Length(arr))); {2}
end;
--------------------------------------------------------------------------------

//没想到可以这样:
const
arr: array[Boolean] of Char = ('A','B');
begin
ShowMessage(arr); {AB}
ShowMessage(IntToStr(Length(arr))); {2}

{访问元素}
ShowMessage(arr[False]); {A}
ShowMessage(arr[True]); {B}

{也可以这样访问}
ShowMessage(arr[Low(arr)]); {A}
ShowMessage(arr[High(arr)]); {B}

{但不能这样访问}
// ShowMessage(arr[0]);
// ShowMessage(arr[1]);

{但可以变通一下}
ShowMessage(arr[Boolean(0)]); {A}
ShowMessage(arr[Boolean(1)]); {B}
end;
--------------------------------------------------------------------------------

//同理, 这样也可以:
const
arr: array[Byte] of Integer = (
1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,
30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,
56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,
82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,
106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,
126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,
146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,
166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,
186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,
206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,
226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,
246,247,248,249,250,251,252,253,254,255,256);
begin
ShowMessage(IntToStr(arr[Low(arr)])); {1}
ShowMessage(IntToStr(arr[High(arr)])); {256}
ShowMessage(IntToStr(Length(arr))); {256}
end;
--------------------------------------------------------------------------------

//给这种用法来一个必要性的实例:
const
BoolStr: array[Boolean] of string = ('False', 'True');
var
b: Boolean;
begin
b := True;
ShowMessage(BoolStr[b]); {True}
b := not b;
ShowMessage(BoolStr[b]); {False}
end;

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