下面函数定义中正确的是 A $x = "OK"; function func(string $a=$x, string $b): string { return $a . $b; } B $x = "OK"; function func(string $a, string $b=$x): string { return $a . $b; } C function func(string $a="OK", string $b): string { return $a . $b; } D function func(string $a, string $b="OK"): string { return $a . $b; }
Question
下面函数定义中正确的是 A $x = "OK";
function func(string x, string $b): string {
return b;
}
B $x = "OK";
function func(string b=$x): string {
return b;
}
C function func(string b): string {
return b;
}
D function func(string b="OK"): string {
return b;
}
Solution
在这四个函数定义中，只有选项C和选项D是正确的。
在PHP中，函数的默认参数值必须是常量表达式，不能是变量，表达式或函数调用。
所以选项A和选项B都是错误的，因为它们试图将变量$x作为默认参数值。
选项C和选项D是正确的，因为它们的默认参数值是常量字符串"OK"。
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