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Output parameters
Like reference parameters, output
parameters don't create a new storage location, but use the storage location of
the variable specified on the invocation. Output parameters need the out
modifier as part of both the declaration and the invocation - that means it's
always clear when you're passing something as an output parameter. Output
parameters are very similar to reference parameters. The only differences
are:
------> The variable specified on
the invocation doesn't need to have been assigned a value before it is passed to
the function member. If the function member completes normally, the variable
is considered to be assigned afterwards (so you can then "read" it).
------> The parameter is considered
initially unassigned (in other words, you must assign it a value before you can
"read" it in the function member).
------> The parameter must be
assigned a value before the function member completes normally. Here is some
example code showing this, with an int parameter (int is a value type, but if
you understood reference parameters properly, you should be able to see what
the behaviour for reference types is):
void Foo (out int x)
{
//
Can't read x here - it's considered unassigned
// Assignment - this must
happen before the method can complete normally
x = 10;
// The
value of x can now be read:
int a = x;
}
...
// Declare a variable but don't assign a
value to itint y;
// Pass it in as an output parameter, even though its
value is
unassignedFoo (out y);
// It's now assigned a value, so we can
write it out:Console.WriteLine (y);
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