Array Subscript Zero

ID

swift.array_subscript_zero

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Swift

Tags

collections, reliability

Description

Reports a subscript expression of the form <expr>[0]. For arrays, prefer .first — it returns an Optional, so accessing the head of an empty collection produces nil instead of crashing.

let head = xs[0]               // FLAW
let nested = xs[0][0]          // FLAW (two)

if let head = xs.first { ... } // OK
print(xs[1])                   // OK — non-zero literal
print(xs[xs.count - 1])        // OK — non-literal
print(xs[0..<2])               // OK — range subscript

Rationale

array[0] traps at runtime if the array is empty. .first returns Optional.none and lets callers decide how to handle the empty case.

Remediation

Use .first and unwrap with if let or guard let:

guard let head = xs.first else {
    return
}
process(head)

References