len() Builtin

The len() builtin returns the length of arrays, maps, and strings.

• Signature: len(value any) -> int
• Supported types: arrays, maps, strings
• Strict behavior: calling len(None) or len() with unsupported types raises a runtime error.

Quick examples

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package main
import fmt

function main() {
    // Arrays
    var a = [1, 2, 3]
    fmt.Println(len(a))      // 3

    // Maps
    var m = {"a": 1, "b": 2}
    fmt.Println(len(m))      // 2

    // Strings
    var s = "hello"
    fmt.Println(len(s))      // 5
}

Strict error behavior

The builtin performs strict type checking. If called with None or any unsupported type, it raises a runtime error.

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package main
import fmt

function main() {
    var x = None
    // This raises a runtime error:
    // "len() argument must be an array, map, or string, got NULL"
    fmt.Println(len(x))
}

Common unsupported arguments: - Integers, floats, booleans - Structs without a string representation as a sequence - None (strictly rejected)

Practical patterns

• Array bounds and iteration:

  Array Bounds and Iteration
  1 2 3	for i in range(len(a)) { // ... }

• Map size checks:

  Map Size Checks
  1 2 3	if len(m) == 0 { fmt.Println("map is empty") }

• String processing:

  String Processing
  1	if len(s) > 80 { /* wrap */ }

Notes

• Behavior mirrors the language’s strict runtime type validation. Use explicit conditionals to check for None before calling len when inputs may be missing.