Someone asked me the other day when they should use the parameter keyword out instead of ref. While I (I think) understand the difference between the ref and out keywords (that has been asked before) and the best explanation seems to be that ref == in and out, what are some (hypothetical or code) examples where I should always use out and not ref.
Since ref is more general, why do you ever want to use out? Is it just syntactic sugar?
How to use in or out or ref in C#?
C# have the same functionality but with some boundaries.in arguments cannot be modified by the called method.ref arguments may be modified.ref must be initialized before being used by caller it can be read and updated in the method.out arguments must be modified by the caller.out arguments must be initialized in the methodin arguments must be initialized before being passed in a method call. However, the called method may not assign a value or modify the argument.You can't use the in, ref, and out keywords for the following kinds of methods:
async modifier.yield return or yield break statement.Still feel the need for a good summary, this is what I came up with.
When we are inside the function, this is how we specify the variable data access control,
in = R
out = must W before R
ref = R+W
in
Function may only READ that variable.
out
Variable must not be initialised first because,
function MUST WRITE to it before READ.
ref
Function may READ/WRITE to that variable.
Focusing on where data gets modified,
in
Data must only be set before entering (in) function.
out
Data must only be set before leaving (out) function.
ref
Data must be set before entering (in) function.
Data may be set before leaving (out) function.
It should be noted that in is a valid keyword as of C# ver 7.2:
The in parameter modifier is available in C# 7.2 and later. Previous versions generate compiler error CS8107 ("Feature 'readonly references' is not available in C# 7.0. Please use language version 7.2 or greater.") To configure the compiler language version, see Select the C# language version.
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The in keyword causes arguments to be passed by reference. It makes the formal parameter an alias for the argument, which must be a variable. In other words, any operation on the parameter is made on the argument. It is like the ref or out keywords, except that in arguments cannot be modified by the called method. Whereas ref arguments may be modified, out arguments must be modified by the called method, and those modifications are observable in the calling context.