Macro create_func 

macro_rules! create_func {
    ($UDF:ident, $SCALAR_UDF_FN:ident) => { ... };
    ($UDF:ident, $SCALAR_UDF_FN:ident, $CTOR:path) => { ... };
}

Creates a singleton ScalarUDF of the $UDF function named STATIC_$(UDF) and a function named $SCALAR_UDF_FUNC which returns that function named STATIC_$(UDF).

This is used to ensure creating the list of ScalarUDF only happens once.

Arguments

• UDF: name of the ScalarUDFImpl
• SCALAR_UDF_FUNC: name of the function to create (just) the ScalarUDF
• (optional) $CTOR: Pass a custom constructor. When omitted it automatically resolves to $UDF::new().