Proposal: Extend the ^ operator
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Michał Muskała
Dec 7, 2016, 11:40:27 AM12/7/16
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Hello everybody,
Today the hat/pin operator (^) only allows the variable as argument, but I think it would be completely valid for it to allow any expression. This feels like a natural extension, especially useful when dealing with map fields. The number of times I tried to write something like that, only to realise it will fail is "too damn high" :P
assert_received {:foo, ^map.foo}
The obvious fix is to transform this into
foo = map.foo
assert_received {:foo, ^foo}
But I wonder - couldn't this be done automatically by the compiler, to extract such things from the patterns in order to place them before the case expression? I could be missing something, especially around some semantic difference, but I though about this for some time, and couldn't see anything harmful.
Michał.
Today the hat/pin operator (^) only allows the variable as argument, but I think it would be completely valid for it to allow any expression. This feels like a natural extension, especially useful when dealing with map fields. The number of times I tried to write something like that, only to realise it will fail is "too damn high" :P
assert_received {:foo, ^map.foo}
The obvious fix is to transform this into
foo = map.foo
assert_received {:foo, ^foo}
But I wonder - couldn't this be done automatically by the compiler, to extract such things from the patterns in order to place them before the case expression? I could be missing something, especially around some semantic difference, but I though about this for some time, and couldn't see anything harmful.
Michał.
José Valim
Dec 7, 2016, 12:03:32 PM12/7/16
to elixir-l...@googlegroups.com
The problem is doing so inside case, receive, etc:
case var do
{:ok, ^map.foo} -> ...
{:error, ^map.bar} -> ...
end
The only way to implement this is by reading the value before the case and that would be counter intuitive.
Michał.
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