Delphi：函数for循环期间没有清空 [英] Delphi: function Result not emptied during for loop

问题描述

是否正常？

for a := 1 to 10 do
    x.test;

   x.test;
   x.test;
   x.test;

function test: string;
begin
  {$IFDEF DEBUG}  DebugMessage('result check = '+Result,3); {$ENDIF}
   result := result + 'a';
end;

10:39:59: result check = 
10:39:59: result check = a
10:39:59: result check = aa
10:39:59: result check = aaa
10:39:59: result check = aaaa
10:39:59: result check = aaaaa
10:39:59: result check = aaaaaa
10:39:59: result check = aaaaaaa
10:39:59: result check = aaaaaaaa
10:39:59: result check = aaaaaaaaa

10:39:59: result check = 
10:39:59: result check = 
10:39:59: result check = 

在for循环中函数结果堆栈不被释放？ ：O

function result stack is not freed during a for loop? :O

推荐答案

结果被视为隐式 var 参数到你的函数。

Result is treated as an implicit var parameter to your function.

想象一下，如果你这样明确写出来：

Imagine if you wrote it out explicitly this way:

procedure test(var result: string);
begin
  result := result + 'a';
end;

for i := 1 to 10 do
  test(s);

然后你会期望它附加到 s 。

Then you would expect it to append to s.

每次你调用它时，你都会抛出 Result 这个事实是为什么编译器有时会决定完成它正如@gabr所指出的那样，它作为优化选择不在循环内完成这个隐式变量。

The fact that you are throwing away Result each time you call it is why the compiler sometimes decides to finalise it. As @gabr points out, it elects not to finalize this implicit variable when inside a loop as an optimisation.

如果要分配 test 到每个你调用 test 的字符串，那么你会看到字符串每次都变长，它永远不会被重新初始化。

If you were to assign the result of test to a string every time you called test then you'd see the string get longer each time, it would never be re-initialized.

这就是为什么你应该总是初始化你的结果变量。它看起来像一个局部变量，但最好被认为是一个 var 参数。

This is why you should always initialize your result variable. It looks like a local variable, but it is best thought of as a var parameter.

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