Feature name

Goto statement

Summary

goto statement for jumps and making scripting a bit easier.

Motivation

Problems

Breaking in nested loops

Let's say for example:

while true do
    for i=1, 100 do
        if (i == 10) then
            break -- This will only break the current for loop
        end
    end
end

In Luau there isn't a easy/simple way to break nested loops(without a variable)

Current solution we have:

local RunLoop = true
while RunLoop do
    for i=1, 100 do
        if (i == 10) then
            RunLoop = false
            break
        end
    end
end

The problems that this solution has are: Messy: In a bigger scale this will get messy and confusing.
Uneeded checks: Why to do those checks when we could just jump out directly?

Possible solution

A goto statement would make Luau more easy to script and cleaner, if used properly.

while true do
    for i=1, 100 do
        if (i == 10) then
            goto LoopEnd         
        end
    end
end
LoopEnd: -- Could follow Lua syntax(:LABEL:)

Design

<ConstantString>: Sets a label
Notes:
A label can't be used in another scope

function A()
    FunctionStart:
        
    do
        if Y == Y then
            goto FunctionStart -- However, this would work
        end
    end

    if X == X then
        goto FunctionStart -- This would act the same as a while loop.
    end
end

function B()
    goto FunctionStart -- Undefined label compile error
end

goto <ConstantString> Jumps to a set label

goto <Number> Jumps to X line Notes:
If the number is a constant number, the compiler should optmize it
Otherwise if the number is a variable, any registers needed should be saved before the jump
If the X line is in another scope a error should be thrown

Drawbacks

Cross thread jumping could be a problem(but it would be very interesting if implemented and used correctly).
Lambdas/Functions that are called could bypass the scope boundary without runtime checks.

Alternatives

A break for nested loops

while true do
    for i=1, 100 do
        if (i == 10) then
            :break -- The ':' means "break depth"
        end
    end
end

2.3 KiB Raw Blame History