c# - Why ref parameters can not be ignored like out parameters? -

is there specific reason why c# 7 bring inlining out parameters not ref?

the following valid on c# 7:

int.tryparse("123", out _); 

but invalid:

public void foo(ref int x) { }  foo(ref _); // error 

i don't see reason why same logic can't applied ref parameters.

the reason simple: because you're not allowed pass uninitialized variable ref parameter. has been case, , new syntactical sugar in c#7 doesn't change that.

observe:

int i; myoutparametermethod(out i);  // allowed  int j; myrefparametermethod(ref j);  // compile error 

the new feature in c#7 allows create variable in process of calling method out parameter. doesn't change rules uninitialized variables. purpose of ref parameter allow passing already-initialized value method , (optionally) allow original variable changed. compiler semantics inside method body treat ref parameters initialized variables , out parameters uninitialized variables. , remains way in c#7.