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Void Type — void

Overview

void is a C FFI-only return type in Nitpick. It indicates that a C function returns no value. Unlike most languages, void is not a general-purpose "no value" type in Nitpick — that role is served by NIL.

Important: You cannot declare void variables, use void as a function return type outside extern blocks, or capture the result of a void-returning function.

Usage: Extern Blocks Only

extern "libc" {
    func:free = void(int64:ptr);         // valid: C function returns nothing
    func:printf = void(string:fmt, ..?); // valid: variadic C function
};

What Gets Rejected

void as a Nitpick function return type

func:do_nothing = void() {    // ❌ REJECTED
    // ...
};

Error: void return type only allowed in extern blocks. Use NIL for no-value returns in Nitpick code.

Capturing the result of a void function

extern "libc" {
    func:free = void(int64:ptr);
};

int32:result = free(ptr);    // ❌ NITPICK-VOID-001

Error: cannot use the result of a void-returning function as an initializer — void functions produce no value.

Declaring void variables

void:x = 42;    // ❌ Parser error

Error: Cannot declare variables of type 'void'.

NIL vs void — When to Use Which

This is the most common point of confusion for new Nitpick programmers:

NIL void
What it is A value meaning "nothing" A type meaning "no return"
Where it's valid Anywhere a value is expected Only in extern block return types
Use case "This function has no meaningful return" "This C function returns nothing"
Result wrapping pass(NIL) → Result<NIL> Not wrapped — raw C ABI
Can be stored Yes (any:x = NIL;) No (cannot declare void variables)
Example func:f = int32() { pass(NIL); }; extern func:f = void(int32:x);

The Design Rationale

Nitpick's Result system wraps every non-extern function return in Result<T>. The NIL value fits naturally into this system — pass(NIL) produces a successful Result<NIL>.

void exists solely for C compatibility. C's void return type means "no return value at the ABI level" — there is literally no register or stack slot allocated for a return value. This is a fundamentally different concept from "I am returning a value that represents nothing."

Diagnostics

ID Trigger Guidance
NITPICK-VOID-001 int32:x = void_func(); Cannot capture void return — void produces no value
NITPICK-VOID-002 x = void_func(); Cannot assign void return — void produces no value

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