parameter-resolution.md

Automatic Parameter Resolution

The invoker inspects each parameter of the callable via reflection and resolves its value automatically. You provide a context array and the resolver chain does the rest.

How It Works

When you call invoke(), the invoker iterates over the callable's parameters and tries each registered resolver in order until one succeeds:

$invoker = new CallableInvoker();

$result = $invoker->invoke(
    callable: fn (?string $title, string $name, int $age = 25) => "$title $name, age $age",
    context: ['name' => 'Alice'],
);

// Result: " Alice, age 25"

For each parameter:

• $title — not in context, no default, but nullable so resolves to null
• $name — matched by name in the context array
• $age — not in context, falls back to its default value 25

Built-in Resolvers

The default resolver chain includes four resolvers, applied in this order:

Resolver	Condition	Result
UnsupportedParameterValueResolver	Variadic or untyped parameter	Throws a specific exception
ContextParameterValueResolver	Parameter name exists in context	Returns $context[$name]
DefaultValueParameterValueResolver	Parameter has a default value	Returns the default value
NullableParameterValueResolver	Parameter allows null	Returns null

If no resolver handles the parameter, a ParameterNotSupportedException is thrown.

Context Array

The context array maps parameter names to values:

$invoker->invoke(
    callable: fn (string $greeting, string $name) => "$greeting, $name!",
    context: ['greeting' => 'Hello', 'name' => 'World'],
);

// Result: "Hello, World!"

Context values take precedence over default values:

$invoker->invoke(
    callable: fn (string $name = 'World') => "Hello, $name!",
    context: ['name' => 'PHP'],
);

// Result: "Hello, PHP!"

Default Values

Parameters with default values are resolved automatically when no context is provided:

$invoker->invoke(
    callable: fn (string $name = 'World', int $count = 3) => str_repeat("Hello, $name! ", $count),
);

// Result: "Hello, World! Hello, World! Hello, World! "

Nullable Parameters

Nullable parameters resolve to null as a last resort:

$invoker->invoke(
    callable: fn (?string $name) => $name ?? 'anonymous',
);

// Result: "anonymous"