07 · Pattern Matching
Defaults while destructuring
A field pattern such as { retries = 3 } supplies a lazy default for optional absence or nil. Zero, false and empty strings remain values. The default runs only when it is needed.
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A field pattern such as { retries = 3 } supplies a lazy default for optional absence or nil. Zero, false and empty strings remain values. The default runs only when it is needed.
Complete example
Defaults while destructuring.
06-destructure-defaults.zolo
struct Settings { timeout: int?, retries: int?, enabled: bool? }
let fallbacks = 0
fn default_timeout() -> int { fallbacks += 1; return 5 }
fn configure(settings: Settings) -> str {
let { timeout: wait = default_timeout(), retries = 3, enabled = true } = settings
assert(wait == 5)
assert(retries == 0)
assert(enabled == false)
"timeout={wait}, retries={retries}, enabled={enabled}"
}
print(configure(Settings { timeout: nil, retries: 0, enabled: false }))
assert(fallbacks == 1)
Reference
zolo run examples/features/40-syntax-fourth/06-destructure-defaults.zolo --no-cache
See also