[Issue 15056] [REG2.068.1] Unstored RAII struct return yields bogus error: "cannot mix core.std.stdlib.alloca() and exception handling"

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15056

Martin Nowak <code at dawg.eu> changed:

           What    |Removed                     |Added
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                 CC|                            |code at dawg.eu

--- Comment #4 from Martin Nowak <code at dawg.eu> ---
But the error message seems correct, default arguments are passed from the
caller site and b/c of the destructor a try catch block is needed around
statements that might throw.

> This idiom allows for concise code that executes extremely fast and uses the least possible amount of stack memory

Not exactly sure why alloca doesn't work with EH handling, but I guess we need
fixed addresses for variables to unwind them.
You could pass in a buffer to avoid alloca.

ubyte[1234] buf = void;
foo(buf.ptr);

It's even possible to wrap the buffer with the function return value.

auto withBuf(size_t n, alias func, Args...)(auto ref Args args)
{
    static struct Result
    {
        ubyte[n] __buf;
        ReturnType!func val;
        alias val this;
    }
    Result res = void;
    emplace(res.val, func(res.ptr, args));
    return res;
}

I'll still try to find out whether 2.068.1 broke something unintentionally.

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