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Method overloads

Lua has no static types, so same-name multiple signatures cannot be chosen at compile time. ZLua provides: default dispatch, full-signature keys (automatic at Bind), [LuaAlias], and register_method short names. See: Demo.Run, app.lua.

Day-to-day demo:Run(10) is enough in Lua calling C#; read this page for ambiguity or hot paths. Authoritative details: Overload Spec.

How to choose​

ApproachSyntaxWhen
Default dispatchdemo:Run(10)Arguments uniquely match
Full-signature key (automatic)demo['Run(System.Int32)'](demo, 5)Exact pick; no register_method needed
[LuaAlias]demo:run_i32(5)You can edit C#; short name on hot paths
register_methodAfter register: demo:run_i32(5)Cannot edit C#; still want short name + colon

Default dispatch​

demo:Run(10)        -- Run(int)
demo:Run("hello")   -- Run(string)

Zero dispatch when there is only one public overload; with multiple, match by arguments.

Default parameters​

C# trailing optional formals (HasDefault) are supported. Lua arg count may fall in [minArity, maxArity]; omitted trailing formals are filled with C# defaults at invoke (cached at Bind; hot path does not parse metadata blobs).

public static int Foo(int x, int y = 5) => x + y;
public static string Bar(string s, int a = 1, int b = 2) => $"{s}:{a},{b}";
public static int G(int x) => x;
public static int G(int x, int y = 5) => x + y;
Demo.Foo(1)          -- y=5
Demo.Foo(1, 9)
Demo.Bar("hi")       -- a=1, b=2
Demo.Bar("hi", 7)    -- b=2
Demo.G(1)            -- pick G(int), not the “expand defaults” G(int,int)
Demo.G(1, 4)         -- G(int, int)
RuleNotes
Trailing contiguous defaults onlySame as C#: cannot “skip” a required formal in the middle
Too few argsCannot cover the first non-default formal → argument mismatch / no matching overload
Multi-overload tie-breakWhen conversion scores tie, the candidate that uses fewer defaults wins
ConstructorsType(...) / SMT.__call support the same rules

Authoritative details: Overload Spec §3.3.

Full-signature keys (auto-registered on name conflicts)​

When the same method name has multiple overloads (e.g. Run(int) / Run(string)), besides the Run dispatch, Bind also hangs a direct key for each candidate:

MethodName(parameter Type.FullName, …) (no return type):

KeyMeaning
RunRuntime dispatch
Run(System.Int32)Fixed Run(int)
Run(System.String)Fixed Run(string)
-- 精确调用，不必 register_method
demo['Run(System.Int32)'](demo, 5)
demo['Run(System.String)'](demo, "hi")

Keys contain parentheses, so you cannot write demo:Run(System.Int32)(...); use bracket keys + dot + explicit self.

[LuaAlias]​

[LuaAlias("run_i32")]
public void Run(int value) { }

public void Run(string value) { }
demo:run_i32(10)    -- 短名 + 冒号，O(1)；Run(int) 已换名，不再挂 "Run"
demo:Run("hi")      -- 未换名的 Run(string)

An alias is a rename (replaces the default Lua key), not an append. XML (luaAliasXmlPaths / ZLuaAlias) and more examples: LuaAlias. C# extensions on the instance table: Extension methods.

register_method: short name + colon​

Full-signature keys already allow exact calls, but the syntax is verbose. register_method hangs a direct closure onto an unused short name; then you can use colon:

local run_i32 = demo['Run(System.Int32)']
zlua.register_method("run_i32", run_i32)

-- 好处：短名进入 method 表，之后直接
demo:run_i32(5)

Two-argument form (per 05-LIB): zlua.register_method(aliasName, directClosure). If aliasName already exists (including Run, full-signature keys, other aliases) → error; no overwrite.

You can also take a closure from a [LuaAlias] key and hang another custom name.

Common mistakes​

SymptomFix
Wrong overload / ambiguousFull-signature key, [LuaAlias], or register_method short name; watch default-parameter tie-break
argument mismatch (with defaults)Required formals not supplied; cannot skip middle parameters
Want demo['(System.Int32)']Forbidden; must include the method name: Run(System.Int32)
register_method says already takenPick an unused alias; do not overwrite Run / existing full-signature keys

Learning path​

Previous0GC Marshal
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