Propose: Syntax-types-number-literals.md #112
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| ### Generic Constraints | ||
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| Number literal types can be used as generic constraints: | ||
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| ```lua | ||
| local function createArray<T, N: number>(value: T, length: N): {T} | ||
| local arr = {} | ||
| for i = 1, length do | ||
| arr[i] = value | ||
| end | ||
| return arr | ||
| end | ||
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| local arr1 = createArray("hello", 3) -- OK: Creates array of length 3 | ||
| local arr2 = createArray("world", -1) -- Type error: Negative length | ||
| ``` |
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This section describes features which do not exist in Luau.
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So sorry about that, I meant something like this:
local function createArray<T, N: 1 | 2 | 3>(value: T, length: N): {T}
local arr = {}
for i = 1, length do
arr[i] = value
end
return arr
end
local arr1 = createArray("hello", 3) -- OK: Creates array of length 3
local arr2 = createArray("world", 4) -- Type error: 4 is not compatible with '1 | 2 | 3'Again, I apologise for that. No idea where my head was at.
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Generic constraints do not exist in Luau at all. <N: 1 | 2 | 3> is not legal syntax right now.
| 4. ***Type Explosion!*** Developers might create excessive unions of number literal types, leading to verbose type annotations. | ||
| 5. ***Limited Usefulness***: In many cases, using enums or string literal types might be more appropriate and readable than number literal types. | ||
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| ## Alternatives |
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I would add "implement this only for integers" as an option. Decimals could get pretty scary.
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Integer literals is a viable alternative, yeah.
| end | ||
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| local function isEven(n: number): 0 | 1 | ||
| return n % 2 |
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Woah, do we expect this will just work without more explicit casts? Your later writing suggests mathematical cases like this are NOT inferred. If that's not the case then you'll need to be more explicit that % does work like this.
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Actually this type isn't even correct. 0.5 % 2 == 0.5.
| local function setVolume(level: 0 | 1 | 2 | 3 | 4 | 5): boolean | ||
| -- Only accepts volume levels 0-5 |
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As written, this would accept the literal integers, 0, 1, 2, 3, 4, and 5, not all numbers on the range [0, 5]
| The type checker will infer the most specific type when dealing with number literals: | ||
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| ```lua | ||
| local x = 42 -- Inferred as '42', not 'number' | ||
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| local function double(n) | ||
| return n * 2 | ||
| end | ||
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| local y = double(5) -- Inferred as 'number', not '10' | ||
| ``` |
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This is a huge departure from how type inference works today for every singleton type. We default to inferring string and boolean, unless the context requires that the singleton type be inferred.
| ### Generic Constraints | ||
|
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||
| Number literal types can be used as generic constraints: | ||
|
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||
| ```lua | ||
| local function createArray<T, N: number>(value: T, length: N): {T} | ||
| local arr = {} | ||
| for i = 1, length do | ||
| arr[i] = value | ||
| end | ||
| return arr | ||
| end | ||
|
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| local arr1 = createArray("hello", 3) -- OK: Creates array of length 3 | ||
| local arr2 = createArray("world", -1) -- Type error: Negative length | ||
| ``` |
There was a problem hiding this comment.
Generic constraints do not exist in Luau at all. <N: 1 | 2 | 3> is not legal syntax right now.
| 4. ***Type Explosion!*** Developers might create excessive unions of number literal types, leading to verbose type annotations. | ||
| 5. ***Limited Usefulness***: In many cases, using enums or string literal types might be more appropriate and readable than number literal types. | ||
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| ## Alternatives |
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Integer literals is a viable alternative, yeah.
| These can be combined with union types to represent a set of allowed values: | ||
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| ```lua | ||
| type HttpSuccessCode = 200 | 201 | 202 | 204 |
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I think this is a bad motivating example.
HTTP defines all 2xx codes to be in the successful category.
Will this RFC make people write more error-prone code like this?
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