presto-main/src/main/java/io/prestosql/metadata/FunctionRegistry.java/FunctionRegistry/ApplicableFunction
class FunctionRegistry:        private ApplicableFunction(FunctionId functionId, Signature declaredSignature, Signature boundSignature)
        {
            this.functionId = functionId;
            this.declaredSignature = declaredSignature;
            this.boundSignature = boundSignature;
        }