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. Individual entries may be a reactive()/reactiveVal.
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. Reactive entries are validated on their resolved value.

Value

The resolved default value or fallback.

Details

Entries that are a shiny::reactive() or shiny::reactiveVal() are resolved with shiny::isolate() before validation, so this returns the reactive's current value. See setup_reactive_defaults() for how modules keep such entries live at render time.

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
get_default(list(color = shiny::reactiveVal("blue")), "color", "black")
#> [1] "blue"