[allocator.requirements.general]/37

Throws: allocate may throw an appropriate exception.

Any limitations on "appropriate" implied elsewhere?

Can a valid custom allocator just throw a double on any request?

Context: implementation of a noexcept function that uses allocator, but has fallback strategy to do something if all allocations fail.

CodePudding user response：

Any limitations on "appropriate" implied elsewhere?

No. "Appropriate" qualifier has no objective meaning. It's effectively a suggestion to use common sense. There are no limitations on the type thrown from allocate.

Can a valid custom allocator just throw a double on any request?

It would be conforming if the author considers double to be appropriate. I wouldn't consider it "appropriate" myself, but it's up to the author to decide.

Context: implementation of a noexcept function that uses allocator, but has fallback strategy to do something if all allocations fail.

You should use a catch-all block:

try {
    ptr = a.allocate();
} catch(...) {
    // deal with it
}