Issue 16168 - isCopyable trait for value types

[BradleyChatha]

This is the first time I've contributed code to a project(other than a slight documentation improvement), so I'm sorry if I've messed up something.

https://issues.dlang.org/show_bug.cgi?id=16168

[dlang-bot]

Fix	Bugzilla	Description
✗	16168	isCopyable trait for value types

[wilzbach]

This is the first time I've contributed code to a project(other than a slight documentation improvement)

That's great to hear!

so I'm sorry if I've messed up something.

Do you see the failing CI integrations?
If you click on them you see why they are failing. It looks like it's just a style issue ;-)

[MetaLang]

You should also check whether S is an interface using !is(S == interface). Please also a test to check whether a class and an interface are copyable.

[andralex]

preapproved pending changes

[BradleyChatha]

I'm not sure if it's worth mentioning, but using S foo; S bar = foo; causes isCopyable to be false when using isCopyable!S2 in the unittest. But using S foo = S.init; S bar = foo; makes it true.

Example:
https://dpaste.dzfl.pl/10aa9f47979d

[japplegame]

isCopyable needs frame pointer, because S2 is nested. Just add static before struct definition and tests will pass.
Anyway you should not use S foo; or S foo = S.init; because the default constructor can be disabled and S.init can be overridden. Use S foo = void; instead.
Personally, I prefer

enum isCopyConstructible(T, From = T) = is(typeof({ From from = void; T t = from; }));