Unsafe.SkipInit and out parameter

[sakno]

Many parsing API looks like following:

public static bool TryParse(string input, out SomeType result)
{
}

When method returns false, is it allowed to use Unsafe.SkipInit(out result) instead of result = default? Most callers ignore the result if it returns false so leaving it uninitialized can save some instructions cause by initobj IL instruction.

Moreover, if SomeType is a reference type so it will be initialized as null by the caller.

[EgorBo]

In my view, cases where TryParse fails are (expected to be) rare so it's not that important to optimize. And returning junk in out doesn't look safe. E.g.

TryParse(input, out MyStruct ms);
if (ms.Id != 0) // Id will be some random value in case of failed TryParse
{
...

[stephentoub]

Additionally, there's also a good deal of code that expects a default value to come out when a Try method returns false. Having that default value be garbage would likely lead to a lot of subtle bugs. It would also propagate the "unsafe"ness out to callers without there being any indication that's happening, in that you can then end up with instances that violate whatever constraints their value type constructors try to enforce.

[IS4Code]

More important than what the user might expect from an unused out parameter is what the documentation tells about the method. Most TryParse methods specify that the argument is set to default. This would be a breaking change then.