可選

Marks a named declaration slot (parameter or 類型 field) as voluntary — the caller or provider may omit the value.

Aliases: optional, voluntary

Syntax: <type> <name> 可選 [= default | 或取 default]

Category#

declaration

Related#

• 或取
• 空
• ∪
• 函式
• 類型

Examples#

radix/corpus/sponte/sponte.fab (canonical · keyword)#

Marks a named declaration slot (parameter or 類型 field) as voluntary — the caller or provider may omit the value.

# =============================================================================
# 可選 — Marks a named declaration slot (parameter or 類型 field) as voluntary — the caller or provider may omit the value.
# =============================================================================
#
# What this teaches:
#   • Voluntary parameter syntax — using `可選` to mark function parameters or 類型 fields as optional
#   • Default values — combining `可選` with `vel` to provide fallbacks when the value is omitted
#
# Common mistakes:
#   • confusing 可選 (optional parameter with a default) with ∪ 無 (nullable type) — 可選 marks omission, ∪ 無 marks absence
#
# See also: vel, 無, ∪, 函式, 類型
# =============================================================================



# 可選 — optional parameter / field marker
#
# GRAMMAR:
#   optionalMarker :← '可選'
#
# EXPECTED OUTPUT:
#   No 入口 — declaration or test-runner surface only.
#
# BACKEND:
#   declaration-only optional slots (whitelist: 可選/sponte.fab). Cross-ref: optionalis/optionalis.fab.
#

fn greet(string 名稱, string titulus optional) → string {
    return 名稱
}

fn paginate(int pagina optional coalesce 1) → string {
    return "page"
}

class User {
    var string name
    var string email optional
}