Function attributes
A signature on these pages can carry up to three attributes. They are part of the declaration, not of the body. They tell the compiler and the VM what a call may assume.
Script functions write them in brackets. Natives write them in the declaration string that the binding registers.
const function [pure] square(x: int): int { return x * x }
let f = @[pure] (x) x * xpure
The result depends only on the arguments. The compiler treats a direct call to a pure function as a constant expression, so it may fold the call or keep the result as a constant initializer.
Mark a function pure only when it reads no mutable state and writes none. The VM does not check this. A pure function with a side effect may not be called at all.
Most of math is pure. math.sqrt and math.clamp are pure. math.rand is not, because it changes the seed.
fastcall
A native calling convention. The compiler emits a dedicated call opcode that skips the frame setup, so the native runs on the caller's frame.
A fastcall native has to be a leaf. It must not call back into the VM, and it must push a bounded number of values. Only the binding sets this attribute. Script code cannot add or remove it. It is shown here because a fastcall native does not appear in a stack trace as a frame of its own.
nodiscard
Discarding the return value is an error. A dev build raises Discarding return value of function 'name' with 'nodiscard' attribute. A release build without runtime type checks does not.
Use it when a discarded result means the call was useless, for example on a function that returns a new value instead of changing its argument.