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support for @tupleReturn per overloaded function signature#495

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tomblind merged 2 commits intomasterfrom
tuplereturn-per-signature
Mar 26, 2019
Merged

support for @tupleReturn per overloaded function signature#495
tomblind merged 2 commits intomasterfrom
tuplereturn-per-signature

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@tomblind tomblind commented Mar 25, 2019

This adds support for per-signature @tupleReturn directives. This allows declaring a function with overloads where some return multiple values, and some do not.

Example:

declare function foo(n: number): number;
/** @tupleReturn */ declare function foo(s: string): [string, string];

const n = foo(1);
const [s1, s2] = foo("bar");

This also works on function types declared as interfaces:

interface Fn {
    (n: number): number;
    /** @tupleReturn */ (s: string): [string, string];
}

Note that if @tupleReturn is placed on the interface itself, it affects all signatures in it:

/** @tupleReturn */
interface Fn {
    (n: number): [number, number];
    (s: string): [string, string];
}

If a function implementation has overloaded declarations, and at least one of those signatures has the @tupleReturn directive, then any array-like return values will be unpacked upon return. Non-array values won't.

Example:

function foo(n: number): number;
/** @tupleReturn */ function foo(s: string): [string, string];
function foo(a: number | string): number | [string, string] {
    if (typeof a === "number") {
        return a;
    } else {
        return [a, "bar"];
    }
}
const x = foo(1);
const [y, z] = foo("bar");
foo = function(self, a)
    if (((type(a) == "table") and "object") or type(a)) == "number" then
        return a;
    else
        return a, "bar"; -- unpacked
    end
end;
local x = foo(_G, 1);
local y, z = foo(_G, "bar"); -- assumed to be unpacked

@tomblind tomblind merged commit 225c7c1 into master Mar 26, 2019
@tomblind tomblind deleted the tuplereturn-per-signature branch March 26, 2019 12:11
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@Perryvw Perryvw Perryvw approved these changes

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@tomblind @Perryvw