# ApplyIf: Seamless Conditionals for Builder Chains [](https://github.com/bavalpey/apply_if/actions/workflows/tests.yml) [](https://api.reuse.software/info/github.com/bavalpey/apply_if) This crate provides the functions `apply_if` and `apply_if_some` for consuming builders, as well as `apply_if_mut` and `apply_if_some_mut` for mutable builder chains. They allow us to conditionally invoke builder functions while keeping the nice chaining syntax. ## Examples These examples use the [`derive_builder`](https://crates.io/crates/derive_builder) crate to create a builder and show how to use the `apply_if...` functions to conditionally invoke builder functions without breaking the chain. ### Mutable Builders This example uses a mutable builder pattern, which is why `apply_if_mut` and `apply_if_some_mut` are used. ```rust extern crate derive_builder; use derive_builder::Builder; use apply_if::ApplyIf; #[derive(Debug,PartialEq,Builder)] struct Value{ #[builder(default = 123)] first: i32, #[builder(default = 42.)] second: f32, } fn main () { // apply_if_mut only applies the function // if the condition is true let value = ValueBuilder::default() .apply_if_mut(true, |builder| builder.first(100)) .second(1.337) .build() .unwrap(); assert_eq!(value, Value{first: 100, second: 1.337}); let value = ValueBuilder::default() .apply_if_mut(false, |builder| builder.first(100)) .second(1.337) .build() .unwrap(); assert_eq!(value, Value{first: 123, second: 1.337}); // apply_if_some_mut only applies the function // if the optional contains a value let value = ValueBuilder::default() .apply_if_some_mut(Some(100), |builder,val| builder.first(val)) .second(1.337) .build() .unwrap(); assert_eq!(value, Value{first: 100, second: 1.337}); let value = ValueBuilder::default() .apply_if_some_mut(None, |builder,val| builder.first(val)) .second(1.337) .build() .unwrap(); assert_eq!(value, Value{first: 123, second: 1.337}); } ``` ### Immutable Builders This example uses a consuming builder pattern, which is why `apply_if` and `apply_if_some` are used. ```rust extern crate derive_builder; use derive_builder::Builder; use apply_if::ApplyIf; #[derive(Debug,PartialEq,Builder)] #[builder(pattern = "immutable")] struct Value{ #[builder(default = 123)] first: i32, #[builder(default = 42.)] second: f32, } fn main () { // apply_if only applies the function // if the condition is true let value = ValueBuilder::default() .apply_if(true, |builder| builder.first(100)) .second(1.337) .build() .unwrap(); assert_eq!(value, Value{first: 100, second: 1.337}); let value = ValueBuilder::default() .apply_if(false, |builder| builder.first(100)) .second(1.337) .build() .unwrap(); assert_eq!(value, Value{first: 123, second: 1.337}); // apply_if_some only applies the function // if the optional contains a value let value = ValueBuilder::default() .apply_if_some(Some(100), |builder,val| builder.first(val)) .second(1.337) .build() .unwrap(); assert_eq!(value, Value{first: 100, second: 1.337}); let value = ValueBuilder::default() .apply_if_some(None, |builder,val| builder.first(val)) .second(1.337) .build() .unwrap(); assert_eq!(value, Value{first: 123, second: 1.337}); } ``` ## License The code in this repository is licensed under either the [MIT License][mit] or the [Apache License 2.0][apache], at your option. Documentation, specifically the documentation comments and all markdown files, are licensed under the [Creative Commons ShareAlike 4.0 license][cc-by-sa]. Generated files are provided under [CC0-1.0][cc0]. [mit]: LICENSES/MIT.txt [apache]: LICENSES/Apache-2.0.txt [cc-by-sa]: LICENSES/CC-BY-SA-4.0.txt [cc0]: LICENSES/CC0-1.0.txt