Resolve a default value from a named list — get

Looks up key in defaults. If present and passes validator (when supplied), returns the stored value; otherwise returns fallback. Uses standard if/else instead of vectorized ifelse() to avoid silent truncation of multi-valued defaults.

Usage

get_default(defaults, key, fallback, validator = NULL)

Arguments

defaults: A named list of default values, or NULL.
key: Character string — the name to look up.
fallback: The value to return when key is absent or fails validation.
validator: An optional single-argument predicate function (e.g., is.numeric, is.logical). When supplied, the stored value is returned only if validator(value) is TRUE.

Value

The resolved default value or fallback.

Author

Jared Andrews

Examples

get_default(list(color = "red"), "color", "black")
#> [1] "red"
get_default(list(), "missing", 10)
#> [1] 10
get_default(list(n = "x"), "n", 5, is.numeric)
#> [1] 5