From: Ralf Jung Date: Mon, 6 Jul 2015 14:45:34 +0000 (+0200) Subject: some more work on part08, and bigint addition X-Git-Url: https://git.ralfj.de/rust-101.git/commitdiff_plain/ee5a849f625d3bd9bd9bb661428d1c051f285ebe?ds=sidebyside;hp=-c some more work on part08, and bigint addition --- ee5a849f625d3bd9bd9bb661428d1c051f285ebe diff --git a/solutions/src/bigint.rs b/solutions/src/bigint.rs index 120ae6c..2c501c2 100644 --- a/solutions/src/bigint.rs +++ b/solutions/src/bigint.rs @@ -231,8 +231,15 @@ mod tests { fn test_add() { let b1 = BigInt::new(1 << 32); let b2 = BigInt::from_vec(vec![0, 1]); + let b3 = BigInt::from_vec(vec![0, 0, 1]); + let b4 = BigInt::new(1 << 63); assert_eq!(&b1 + &b2, BigInt::from_vec(vec![1 << 32, 1])); + assert_eq!(&b2 + &b1, BigInt::from_vec(vec![1 << 32, 1])); + assert_eq!(&b2 + &b3, BigInt::from_vec(vec![0, 1, 1])); + assert_eq!(&b2 + &b3 + &b4 + &b4, BigInt::from_vec(vec![0, 2, 1])); + assert_eq!(&b2 + &b4 + &b3 + &b4, BigInt::from_vec(vec![0, 2, 1])); + assert_eq!(&b4 + &b2 + &b3 + &b4, BigInt::from_vec(vec![0, 2, 1])); } #[test] diff --git a/src/part08.rs b/src/part08.rs index e01a35b..cacff46 100644 --- a/src/part08.rs +++ b/src/part08.rs @@ -47,15 +47,14 @@ fn test_overflowing_add() { // ## Associated Types //@ Now we are equipped to write the addition function for `BigInt`. As you may have guessed, the `+` operator -//@ is tied to a trait (`std::ops::Add`), which we are now going to implement for `BigInt`. +//@ is tied to a trait (`std::ops::Add`), which we are going to implement for `BigInt`. //@ -//@ In general, addition need not be homogeneous: For example, we could add a vector (in 3-dimensional -//@ space, say) to a point. So when implementing `Add` for a type, one has to specify the type of -//@ the other operand. In this case, it will also be `BigInt` (and we could have left it away, since that's the default). +//@ In general, addition need not be homogeneous: You could add things of different types, like vectors and points. So when implementing +//@ `Add` for a type, one has to specify the type of the other operand. In this case, it will also be `BigInt` (and we could have left it +//@ away, since that's the default). impl ops::Add for BigInt { - //@ Besides static functions and methods, traits can contain *associated types*: This is a type - //@ chosen by every particular implementation of the trait. The methods of the trait can then - //@ refer to that type. In the case of addition, it is used to give the type of the result. + //@ Besides static functions and methods, traits can contain *associated types*: This is a type chosen by every particular implementation + //@ of the trait. The methods of the trait can then refer to that type. In the case of addition, it is used to give the type of the result. //@ (Also see the [documentation of `Add`](http://doc.rust-lang.org/stable/std/ops/trait.Add.html).) //@ //@ In general, you can consider the two `BigInt` given above (in the `impl` line) *input* types of trait search: When @@ -74,9 +73,10 @@ impl ops::Add for BigInt { let mut result_vec:Vec = Vec::with_capacity(max_len); let mut carry = false; /* the current carry bit */ for i in 0..max_len { - // Compute next digit and carry. Store the digit for the result, and the carry for later. let lhs_val = if i < self.data.len() { self.data[i] } else { 0 }; let rhs_val = if i < rhs.data.len() { rhs.data[i] } else { 0 }; + // Compute next digit and carry. Then, store the digit for the result, and the carry for later. + //@ Notice how we can obtain names for the two components of the pair that `overflowing_add` returns. let (sum, new_carry) = overflowing_add(lhs_val, rhs_val, carry); /*@*/ result_vec.push(sum); /*@*/ carry = new_carry; /*@*/ @@ -87,12 +87,12 @@ impl ops::Add for BigInt { } // ## Traits and borrowed types -//@ If you inspect the addition function above closely, you will notice that it actually requires -//@ *ownership* of its arguments: Both operands are consumed to produce the result. This is, of -//@ course, in general not what we want. We'd rather like to be able to add two `&BigInt`. +//@ If you inspect the addition function above closely, you will notice that it actually consumes ownership of both operands +//@ to produce the result. This is, of course, in general not what we want. We'd rather like to be able to add two `&BigInt`. // Writing this out becomes a bit tedious, because trait implementations (unlike functions) require full explicit annotation -// of lifetimes. Make sure you understand exactly what the following definition says. +// of lifetimes. Make sure you understand exactly what the following definition says. Notice that we can implement a trait for +// a borrowed type! impl<'a, 'b> ops::Add<&'a BigInt> for &'b BigInt { type Output = BigInt; fn add(self, rhs: &'a BigInt) -> Self::Output { @@ -106,10 +106,19 @@ impl<'a, 'b> ops::Add<&'a BigInt> for &'b BigInt { //@ considered good style to bundle all tests together. This is particularly useful in cases where //@ you wrote utility functions for the tests, that no other code should use. -// Rust calls a bunch of definitions that are grouped together a *module*. You can put definitions in a submodule as follows. -mod my_mod { - type MyType = i32; - fn my_fun() -> MyType { 42 } +// Rust calls a bunch of definitions that are grouped together a *module*. You can put the tests in a submodule as follows. +//@ The `cfg` attribute controls whether this module is even compiled: If we added some functions that are useful for testing, +//@ Rust would not bother compiling them when you just build your program for normal use. Other than that, tests work as usually. +#[cfg(test)] +mod tests { + #[test] + fn test_add() { + let b1 = BigInt::new(1 << 32); + let b2 = BigInt::from_vec(vec![0, 1]); + + assert_eq!(&b1 + &b2, BigInt::from_vec(vec![1 << 32, 1])); + // **Exercise 08.4**: Add some more cases to this test. + } } //@ As already mentioned, outside of the module, only those items declared public with `pub` may be used. Submodules can access //@ everything defined in their parents. Modules themselves are also hidden from the outside per default, and can be made public @@ -126,25 +135,12 @@ mod my_mod { //@ Modules can be put into separate files with the syntax `mod name;`. To explain this, let me take a small detour through //@ the Rust compilation process. Cargo starts by invoking`rustc` on the file `src/lib.rs` or `src/main.rs`, depending on whether //@ you compile an application or a library. When `rustc` encounters a `mod name;`, it looks for the files `name.rs` and -//@ `name/mod.rs` and goes on compiling there. (It is an error for both of them to exist). You can think of the contents of the +//@ `name/mod.rs` and goes on compiling there. (It is an error for both of them to exist.) You can think of the contents of the //@ file being embedded at this place. However, only the file where compilation started, and files `name/mod.rs` can load modules //@ from other files. This ensures that the directory structure mirrors the structure of the modules, with `mod.rs`, `lib.rs` //@ and `main.rs` representing a directory or crate itself (similar to, e.g., `__init__.py` in Python). -// For the purpose of testing, one typically introduces a module called `tests` and tells the compiler -// (by means of the `cfg` attribute) to only compile this module for tests. -#[cfg(test)] -mod tests { - //@ If we added some functions here that are useful for testing, Rust would not bother compiling - //@ them when you just build your program for normal use. Other than that, tests work as usually. - #[test] - fn test_add() { - let b1 = BigInt::new(1 << 32); - let b2 = BigInt::from_vec(vec![0, 1]); - - assert_eq!(&b1 + &b2, BigInt::from_vec(vec![1 << 32, 1])); - // **Exercise 08.4**: Add some more testcases. - } -} +// **Exercise 08.4**: Write a subtraction function, and testcases for it. Decide for yourself how you want to handle negative results. +// For example, you may want to return an `Option`, to panic, or to return `0`. //@ [index](main.html) | [previous](part07.html) | [next](main.html) diff --git a/workspace/src/part08.rs b/workspace/src/part08.rs index 7e2ba3b..5a5f792 100644 --- a/workspace/src/part08.rs +++ b/workspace/src/part08.rs @@ -46,9 +46,9 @@ impl ops::Add for BigInt { let mut result_vec:Vec = Vec::with_capacity(max_len); let mut carry = false; /* the current carry bit */ for i in 0..max_len { - // Compute next digit and carry. Store the digit for the result, and the carry for later. let lhs_val = if i < self.data.len() { self.data[i] } else { 0 }; let rhs_val = if i < rhs.data.len() { rhs.data[i] } else { 0 }; + // Compute next digit and carry. Then, store the digit for the result, and the carry for later. unimplemented!() } // **Exercise 08.2**: Handle the final `carry`, and return the sum. @@ -59,7 +59,8 @@ impl ops::Add for BigInt { // ## Traits and borrowed types // Writing this out becomes a bit tedious, because trait implementations (unlike functions) require full explicit annotation -// of lifetimes. Make sure you understand exactly what the following definition says. +// of lifetimes. Make sure you understand exactly what the following definition says. Notice that we can implement a trait for +// a borrowed type! impl<'a, 'b> ops::Add<&'a BigInt> for &'b BigInt { type Output = BigInt; fn add(self, rhs: &'a BigInt) -> Self::Output { @@ -70,14 +71,7 @@ impl<'a, 'b> ops::Add<&'a BigInt> for &'b BigInt { // ## Modules -// Rust calls a bunch of definitions that are grouped together a *module*. You can put definitions in a submodule as follows. -mod my_mod { - type MyType = i32; - fn my_fun() -> MyType { 42 } -} - -// For the purpose of testing, one typically introduces a module called `tests` and tells the compiler -// (by means of the `cfg` attribute) to only compile this module for tests. +// Rust calls a bunch of definitions that are grouped together a *module*. You can put the tests in a submodule as follows. #[cfg(test)] mod tests { #[test] @@ -86,7 +80,10 @@ mod tests { let b2 = BigInt::from_vec(vec![0, 1]); assert_eq!(&b1 + &b2, BigInt::from_vec(vec![1 << 32, 1])); - // **Exercise 08.4**: Add some more testcases. + // **Exercise 08.4**: Add some more cases to this test. } } +// **Exercise 08.4**: Write a subtraction function, and testcases for it. Decide for yourself how you want to handle negative results. +// For example, you may want to return an `Option`, to panic, or to return `0`. +