Constant W0001_USED_UNINITIALIZED_VARIABLE

pub const W0001_USED_UNINITIALIZED_VARIABLE: ErrorCode;

W0001: Use of a variable before it has been initialized

A variable declared with let but not initialized defaults to ().

• ✅ Assign a value when declaring (e.g., let a = 5;)
• ✅ Or assign a value before first use (e.g., let a; a = 5; a)

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Example of problematic code

let a;
a;

// autogenerated

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Explanation

When you declare a variable with let but do not give it an initial value, Compose defaults it to the unit value () (similar to void in other languages).

While this is valid syntax, it often indicates a mistake — such as assuming the variable has a meaningful default or forgetting to initialize it before use.

This warning helps prevent subtle logic bugs or no-op evaluations.

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Fixes

✅ Initialize the variable during declaration:

let a = 42;
a

✅ Assign a value before using the variable:

let a;
a = 10;
a

✅ If you meant to use the unit value, make it explicit:

let a = ();
a // evaluates to ()

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Why this matters

Uninitialized variables default to (), which is often unintentional. For example:

let total;
println("Total is", total);

// autogenerated

This will print "Total is ()" — which likely isn’t what you meant.