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96 lines
3 KiB
Markdown
96 lines
3 KiB
Markdown
# math.isnan, math.isinf and math.isfinite for Math Library
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**Status**: Implemented
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## Summary
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This RFC proposes a `math.isnan`, a `math.isinf`, and a `math.isfinite` function to be added to the math library.
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These functions will validate that numbers are not NaN and are "finite" (non-NaN non-inf valid numbers)
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respectively.
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## Motivation
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Currently, determinating if a value is `NaN` requires non-obvious and non-semantic check `x ~= x`. Determining if
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a number is finite requires a verbose check that handles both `NaN` and `Inf` cases, typically like `x == x`
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& `math.abs(x) ~= math.huge`. Checking specifically for Infinity also requires a manual check like
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`math.abs(x) == math.huge`.
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Adding explicit `math.isnan(x)`, `math.isinf(x)` and `math.isfinite(x)` functions brings Luau's math library
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in line with modern languages (such as C++, JavaScript, Python, etc), improving code clarity, robustness and
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safety for mathemetical applications. In networked environments, validating numbers received from the client is a
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must and applicable across most games.
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## Design
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We propose adding three new functions to the global `math` table:
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`math.isnan(x: number): boolean`
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Returns `true` if `x` is Not-a-Number (`NaN`), and false otherwise.
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**Example:**
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```luau
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local x = 0 / 0 -- produces NaN
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local y = 10
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print(math.isnan(x)) -- true
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print(math.isnan(y)) -- false
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```
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`math.isinf(x: number): boolean`
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Returns `true` if `x` is positive or negative infinity (`Inf`), and `false` otherwise.
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**Example:**
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```luau
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local x = math.huge
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local y = 10
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print(math.isinf(x)) -- true
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print(math.isinf(y)) -- false
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print(math.isinf(0 / 0)) -- false (NaN)
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```
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`math.isfinite(x: number): boolean`
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Returns `true` if `x` is a finite number, meaning it is neither `NaN` nor positive or negative infinity
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(`math.huge`).
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**Example:**
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```luau
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local x = math.huge
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local y = 0 / 0
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local z = 123.45
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print(math.isfinite(x)) -- false
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print(math.isfinite(y)) -- false
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print(math.isfinite(z)) -- true
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```
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## Drawbacks
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1. Increased API: This proposal adds three new functions to the global `math` library, increasing the overall
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size of the standard library.
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2. Redundancy for experienced developers: Experienced developers familiary with these checks, may view these
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functions as unnecessary syntactic sugar for the already fast and idiomatic check `x ~= x` and
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`math.abs(x) ~= math.huge`.
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## Alternatives
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### **Alternative 1: Status Quo**
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**Proposal:** Do not add new functions. Continue to rely on checks for both.
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**Rejection:** This sacrifices clarity and developer experience for the sake of library minimalism. The lack of
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standard functions makes code more brittle and harder to read, especially for newcomes to Luau.
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### **Alternative 2: Only add `math.isfinite`**
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**Proposal:** Only add the primary utility check, `math.isfinite(x)`, as it covers the most common use case
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(checking if a number is safe). Users could rely on idioms (`x ~= x`) for `NaN` and (`math.abs(x) == math.huge`)
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for `Inf`.
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