On Sunday, 6 November 2016 at 05:07:10 UTC, Andrei Alexandrescu
wrote:
The declaration with "if" seems to be a recent fashion. I've
first seen it in Go and now C++17 took a shine to it -
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0305r0.html. A DIP would do good to cite that related work.
It seems a low impact feature. Also, the Go/C++ syntaxes seem
suboptimal to me because they are stuttering:
if variable := fun(); variable != 42 {
...
}
or (C++):
if (auto variable = fun(); variable != 42) {
...
}
Why does the word "variable" need to appear twice? It seems
simpler to allow punctuation around existing syntax:
// possible future D
if ((auto variable = fun()) != 42) {
...
}
Defining a variable in an expression wouldn't be allowed
everywhere (but might be contemplated later as an possibility,
which is a nice thing about this syntax).
Andrei
I remember an old suggestion/DIP allowing 'with' statements to
introduce/declare symbols/variables.
Might be a cleaner extension to existing language:
with(auto x = f()) if(foo(x)) {}
else with(auto r = root(t)) if(leaf(r) || blah < bar) {}
