Macro compose_extrinsic 

macro_rules! compose_extrinsic {
    ($api: expr,
	$pallet_name: expr,
	$call_name: expr
	$(, $args: expr) *) => { ... };
}

Generates an UncheckedExtrinsic for the given pallet and call from the metadata.

Returns None if call is not found within metadata. Fetches the nonce from the given api instance. If this fails, zero is taken as default nonce. See also compose_extrinsic_with_nonce