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//Copyright 2016 William Cody Laeder // //Licensed 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. //!Memoization offers a simple generic enum that allows for variables and //!structure fields to become memoized. The generic signature is pretty ugly //!but a user should be able to contain that within a structure. This is a //!fairly powerful pattern. //! //!The deref, derefmut, and borrow fields are overloaded. So as a structure //!field the contained data can be written to, and borrowed much like a normal //!field. //! //!I believe this should be able to be ported to `core`, as none of its codee //!necessarily needs standard. This maybe a future project. use std::marker::PhantomData; use std::clone::Clone; use std::ops::Deref; use std::borrow::Borrow; use std::ops::DerefMut; ///The enumerator that holds data. In its pre-processed state it holds a ///pointer to the lambda that assigns its future constant value. /// /// use memoization::Memoized; /// /// struct Example<I:'static, O: Clone, F: Fn(I) -> O> { /// data: Memoized<I,O,F> /// } /// /// fn eq_str(a: &str, b: &str) -> bool { /// a == b /// } /// /// /// let lambda = |x: i32 | -> String { /// x.to_string() /// }; /// let mut dut = Example { /// data: Memoized::new(lambda) /// }; /// //field is memoized but it can still be written too. /// *dut.data = "9001".to_string(); /// //field can be borrowed as its output data type. /// assert!( eq_str( &dut.data, "9001") ); /// /// pub enum Memoized<I:'static,O:Clone,Func:Fn(I)->O> { UnInitialized(PhantomData<&'static I>,Box<Func>), Processed(O), } impl<I:'static,O:Clone,Func:Fn(I)->O> Memoized<I,O,Func> { ///Build a new memoized field. The user will pass a lambda function ///that will provide the constructor with typing data. /// /// use memoization::Memoized; /// /// let lambda = | a: (i32,i64,&str) | -> String { /// format!("Line {:?} DateCode {:?} Log \"{}\"",a.0,a.1,a.2) /// }; /// /// let memoized = Memoized::new(lambda); /// pub fn new(lambda: Func) -> Memoized<I,O,Func> { Memoized::UnInitialized(PhantomData,Box::new(lambda)) } ///This will convert an UnInitialized value to a Processed value. When ///called on a processed value it will panic. /// /// use memoization::Memoized; /// /// let tup: (i32,i64,&'static str) = (20,-15,"Hello World!"); /// let lambda = | a: (i32,i64,&str) | -> String { /// format!("Line {:?} DateCode {:?} Log \"{}\"",a.0,a.1,a.2) /// }; /// let mut memoized = Memoized::new(lambda); /// //process the data /// memoized.process(tup); /// //borrowing the processed, as it's processed data type /// let x: &str = &memoized; /// assert_eq!( x, "Line 20 DateCode -15 Log \"Hello World!\""); /// pub fn process(&mut self, data: I) { let val = match self { &mut Memoized::Processed(_) => panic!("Already processed"), &mut Memoized::UnInitialized(_,ref z) => z(data) }; *self = Memoized::Processed(val); } ///When passed input data the enum will execute, and return a CLONE of its ///result. The data will be created at this stage. If the data already ///exists it will return a clone of the data. /// /// use memoization::Memoized; /// /// let tup: (i32,i64,&'static str) = (20,-15,"Hello World!"); /// let lambda = | a: (i32,i64,&str) | -> String { /// format!("Line {:?} DateCode {:?} Log \"{}\"",a.0,a.1,a.2) /// }; /// let mut memoized = Memoized::new(lambda); /// //process + fetch a copy /// let output: String = memoized.fetch(tup); /// assert_eq!( output, "Line 20 DateCode -15 Log \"Hello World!\"".to_string()); /// pub fn fetch(&mut self, data: I) -> O { let (flag,val) = match self { &mut Memoized::Processed(ref x) => (false,x.clone()), &mut Memoized::UnInitialized(_,ref z) => (true,z(data)) }; if flag { *self = Memoized::Processed(val.clone()); } val } ///returns a clone of a processed field. If the field is not processed the ///function will panic. /// /// use memoization::Memoized; /// /// let tup: (i32,i64,&'static str) = (20,-15,"Hello World!"); /// let lambda = | a: (i32,i64,&str) | -> String { /// format!("Line {:?} DateCode {:?} Log \"{}\"",a.0,a.1,a.2) /// }; /// let mut memoized = Memoized::new(lambda); /// //process the data /// memoized.process(tup); /// //get copy of the data /// let x: String = memoized.get(); /// assert_eq!( x, "Line 20 DateCode -15 Log \"Hello World!\"".to_string()); /// pub fn get(&self) -> O { match self { &Memoized::Processed(ref x) => x.clone(), _ => panic!("Called get on an uninitialized field") } } ///Informs user if filed has been processed/initalized. /// /// use memoization::Memoized; /// /// let tup: (i32,i64,&'static str) = (20,-15,"Hello World!"); /// let lambda = | a: (i32,i64,&str) | -> String { /// format!("Line {:?} DateCode {:?} Log \"{}\"",a.0,a.1,a.2) /// }; /// let mut memoized = Memoized::new(lambda); /// //data is not initalized/processed /// assert!( ! memoized.is_initialized() ); /// //process the data /// memoized.process(tup); /// //data is now initalized /// assert!( memoized.is_initialized() ); /// pub fn is_initialized(&self) -> bool { match self { &Memoized::Processed(_) => true, _ => false } } } impl<I:'static,O:Clone,Func:Fn(I)->O> Deref for Memoized<I,O,Func> { type Target = O; fn deref<'b>(&'b self) -> &'b Self::Target { match self { &Memoized::Processed(ref x) => x, _ => panic!("Attempted to derefence uninitalized memoized value") } } } impl<I:'static,O:Clone,Func:Fn(I)->O> DerefMut for Memoized<I,O,Func> { fn deref_mut<'b>(&'b mut self) -> &'b mut Self::Target { if self.is_initialized() { match self { &mut Memoized::Processed(ref mut x) => return x, _ => unreachable!() }; } else { *self = Memoized::Processed(unsafe{std::mem::zeroed()}); match self { &mut Memoized::Processed(ref mut x) => return x, _ => unreachable!() }; } } } impl<I:'static,O:Clone,Func:Fn(I)->O> Borrow<O> for Memoized<I,O,Func> { fn borrow<'b>(&'b self) -> &'b O { match self { &Memoized::Processed(ref x) => x, _ => panic!("Attempted to borrow uninitalized memoized value") } } } mod test { use super::Memoized; #[test] fn test_memoized_0() { //build lambda function let lambda = |x: i32| -> String { x.to_string() }; //build object let mut dut = Memoized::new(lambda); //value shouldn't be initialized assert_eq!(dut.is_initialized(), false); //initialized the value assert_eq!(&dut.fetch(5), "5"); //check value is initialized assert_eq!(dut.is_initialized(), true); //check get works assert_eq!(&dut.get(), "5"); //check fetch no longer modifies value assert_eq!(&dut.fetch(2000), "5"); assert_eq!(&dut.get(), "5"); //check on borrow let x: &str = &dut; assert_eq!( x, "5"); } #[test] #[should_panic] fn test_memoized_1() { //build lambda function let lambda = |x: i32| -> String { x.to_string() }; //build object let dut = Memoized::new(lambda); //value shouldn't be initialized assert_eq!(dut.is_initialized(), false); //get object //THIS WILL PANICE assert_eq!(&dut.get(), "5"); } #[test] fn test_memoized_2() { let lambda = |x:i32| -> String { x.to_string() }; let mut dut = Memoized::new(lambda); *dut = "5000".to_string(); assert_eq!(dut.is_initialized(), true); assert_eq!(*dut, "5000"); assert!( eq_str(&dut, "5000")); } fn eq_str(a: &str, b: &str) -> bool { a == b } struct Testing<I:'static,O:Clone,F: Fn(I)->O> { data: Memoized<I,O,F> } #[test] fn test_testing_pattern() { let lambda = |x: i32| -> String { x.to_string() }; let mut dut = Testing { data: Memoized::new(lambda) }; //data doesn't exist yet assert!( ! dut.data.is_initialized()); //assign data *dut.data = "9000".to_string(); //now it is assert!( dut.data.is_initialized()); assert!( eq_str(&dut.data, "9000")); } }