alamb commented on code in PR #8705: URL: https://github.com/apache/arrow-datafusion/pull/8705#discussion_r1474350984
########## datafusion/functions/src/macros.rs: ########## @@ -0,0 +1,123 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +/// macro that exports a list of function names as: +/// 1. individual functions in an `expr_fn` module +/// 2. a single function that returns a list of all functions +/// +/// Equivalent to +/// ```text +/// pub mod expr_fn { +/// use super::*; +/// /// Return encode(arg) +/// pub fn encode(args: Vec<Expr>) -> Expr { +/// super::encode().call(args) +/// } +/// ... +/// /// Return a list of all functions in this package +/// pub(crate) fn functions() -> Vec<Arc<ScalarUDF>> { +/// vec![ +/// encode(), +/// decode() +/// ] +/// } +/// ``` +macro_rules! export_functions { + ($(($FUNC:ident, $($arg:ident)*, $DOC:expr)),*) => { + pub mod expr_fn { + $( + #[doc = $DOC] + /// Return $name(arg) + pub fn $FUNC($($arg: datafusion_expr::Expr),*) -> datafusion_expr::Expr { + super::$FUNC().call(vec![$($arg),*],) + } + )* + } + + /// Return a list of all functions in this package + pub fn functions() -> Vec<std::sync::Arc<datafusion_expr::ScalarUDF>> { + vec![ + $( + $FUNC(), + )* + ] + } + }; +} + +/// Creates a singleton `ScalarUDF` of the `$UDF` function named `$GNAME` and a +/// function named `$NAME` which returns that function named $NAME. +/// +/// This is used to ensure creating the list of `ScalarUDF` only happens once. +macro_rules! make_udf_function { + ($UDF:ty, $GNAME:ident, $NAME:ident) => { + /// Singleton instance of the function + static $GNAME: std::sync::OnceLock<std::sync::Arc<datafusion_expr::ScalarUDF>> = + std::sync::OnceLock::new(); + + /// Return a [`ScalarUDF`] for [`$UDF`] + /// + /// [`ScalarUDF`]: datafusion_expr::ScalarUDF + fn $NAME() -> std::sync::Arc<datafusion_expr::ScalarUDF> { + $GNAME + .get_or_init(|| { + std::sync::Arc::new(datafusion_expr::ScalarUDF::new_from_impl( + <$UDF>::new(), + )) + }) + .clone() + } + }; +} + +/// Macro creates the named module if the feature is enabled +/// otherwise creates a stub +/// +/// Which returns: +/// +/// 1. The list of actual function implementation when the relevant +/// feature is activated, +/// +/// 2. A list of stub function when the feature is not activated that produce +/// a runtime error (and explain what feature flag is needed to activate them). +/// +/// The rationale for providing stub functions is to help users to configure datafusion +/// properly (so they get an error telling them why a function is not available) +/// instead of getting a cryptic "no function found" message at runtime. + +macro_rules! make_package { + ($name:ident, $feature:literal, $DOC:expr) => { + #[cfg(feature = $feature)] Review Comment: Here is a discussion / proposal on how the functions could be organized: https://github.com/apache/arrow-datafusion/issues/9100 -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: github-unsubscr...@arrow.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
