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diff --git a/d.html.markdown b/d.html.markdown new file mode 100644 index 00000000..6f88cf84 --- /dev/null +++ b/d.html.markdown @@ -0,0 +1,260 @@ +--- +language: D +filename: learnd.d +contributors: + - ["Nick Papanastasiou", "www.nickpapanastasiou.github.io"] +lang: en +--- + +```c +// You know what's coming... +module hello; + +import std.stdio; + +// args is optional +void main(string[] args) { + writeln("Hello, World!"); +} +``` + +If you're like me and spend way too much time on the internet, odds are you've heard +about [D](http://dlang.org/). The D programming language is a modern, general-purpose, +multi-paradigm language with support for everything from low-level features to +expressive high-level abstractions. + +D is actively developed by a large group of super-smart people and is spearheaded by +[Walter Bright](https://en.wikipedia.org/wiki/Walter_Bright) and +[Andrei Alexandrescu](https://en.wikipedia.org/wiki/Andrei_Alexandrescu). +With all that out of the way, let's look at some examples! + +```c +import std.stdio; + +void main() { + + // Conditionals and loops work as expected. + for(int i = 0; i < 10000; i++) { + writeln(i); + } + + // 'auto' can be used for inferring types. + auto n = 1; + + // Numeric literals can use '_' as a digit separator for clarity. + while(n < 10_000) { + n += n; + } + + do { + n -= (n / 2); + } while(n > 0); + + // For and while are nice, but in D-land we prefer 'foreach' loops. + // The '..' creates a continuous range, including the first value + // but excluding the last. + foreach(n; 1..1_000_000) { + if(n % 2 == 0) + writeln(n); + } + + // There's also 'foreach_reverse' when you want to loop backwards. + foreach_reverse(n; 1..int.max) { + if(n % 2 == 1) { + writeln(n); + } else { + writeln("No!"); + } + } +} +``` + +We can define new types with `struct`, `class`, `union`, and `enum`. Structs and unions +are passed to functions by value (i.e. copied) and classes are passed by reference. Furthermore, +we can use templates to parameterize all of these on both types and values! + +```c +// Here, 'T' is a type parameter. Think '<T>' from C++/C#/Java. +struct LinkedList(T) { + T data = null; + + // Use '!' to instantiate a parameterized type. Again, think '<T>'. + LinkedList!(T)* next; +} + +class BinTree(T) { + T data = null; + + // If there is only one template parameter, we can omit the parentheses. + BinTree!T left; + BinTree!T right; +} + +enum Day { + Sunday, + Monday, + Tuesday, + Wednesday, + Thursday, + Friday, + Saturday, +} + +// Use alias to create abbreviations for types. +alias IntList = LinkedList!int; +alias NumTree = BinTree!double; + +// We can create function templates as well! +T max(T)(T a, T b) { + if(a < b) + return b; + + return a; +} + +// Use the ref keyword to ensure pass by reference. That is, even if 'a' and 'b' +// are value types, they will always be passed by reference to 'swap()'. +void swap(T)(ref T a, ref T b) { + auto temp = a; + + a = b; + b = temp; +} + +// With templates, we can also parameterize on values, not just types. +class Matrix(uint m, uint n, T = int) { + T[m] rows; + T[n] columns; +} + +auto mat = new Matrix!(3, 3); // We've defaulted type 'T' to 'int'. + +``` + +Speaking of classes, let's talk about properties for a second. A property +is roughly a function that may act like an lvalue, so we can +have the syntax of POD structures (`structure.x = 7`) with the semantics of +getter and setter methods (`object.setX(7)`)! + +```c +// Consider a class parameterized on types 'T' & 'U'. +class MyClass(T, U) { + T _data; + U _other; +} + +// And "getter" and "setter" methods like so: +class MyClass(T, U) { + T _data; + U _other; + + // Constructors are always named 'this'. + this(T t, U u) { + // This will call the setter methods below. + data = t; + other = u; + } + + // getters + @property T data() { + return _data; + } + + @property U other() { + return _other; + } + + // setters + @property void data(T t) { + _data = t; + } + + @property void other(U u) { + _other = u; + } +} + +// And we use them in this manner: +void main() { + auto mc = new MyClass!(int, string)(7, "seven"); + + // Import the 'stdio' module from the standard library for writing to + // console (imports can be local to a scope). + import std.stdio; + + // Call the getters to fetch the values. + writefln("Earlier: data = %d, str = %s", mc.data, mc.other); + + // Call the setters to assign new values. + mc.data = 8; + mc.other = "eight"; + + // Call the getters again to fetch the new values. + writefln("Later: data = %d, str = %s", mc.data, mc.other); +} +``` + +With properties, we can add any amount of logic to +our getter and setter methods, and keep the clean syntax of +accessing members directly! + +Other object-oriented goodies at our disposal +include interfaces, abstract classes, +and overriding methods. D does inheritance just like Java: +Extend one class, implement as many interfaces as you please. + +We've seen D's OOP facilities, but let's switch gears. D offers +functional programming with first-class functions, `pure` +functions, and immutable data. In addition, all of your favorite +functional algorithms (map, filter, reduce and friends) can be +found in the wonderful `std.algorithm` module! + +```c +import std.algorithm : map, filter, reduce; +import std.range : iota; // builds an end-exclusive range + +void main() { + // We want to print the sum of a list of squares of even ints + // from 1 to 100. Easy! + + // Just pass lambda expressions as template parameters! + // You can pass any function you like, but lambdas are convenient here. + auto num = iota(1, 101).filter!(x => x % 2 == 0) + .map!(y => y ^^ 2) + .reduce!((a, b) => a + b); + + writeln(num); +} +``` + +Notice how we got to build a nice Haskellian pipeline to compute num? +That's thanks to a D innovation know as Uniform Function Call Syntax (UFCS). +With UFCS, we can choose whether to write a function call as a method +or free function call! Walter wrote a nice article on this +[here.](http://www.drdobbs.com/cpp/uniform-function-call-syntax/232700394) +In short, you can call functions whose first parameter +is of some type A on any expression of type A as a method. + +I like parallelism. Anyone else like parallelism? Sure you do. Let's do some! + +```c +// Let's say we want to populate a large array with the square root of all +// consecutive integers starting from 1 (up until the size of the array), and we +// want to do this concurrently taking advantage of as many cores as we have +// available. + +import std.stdio; +import std.parallelism : parallel; +import std.math : sqrt; + +void main() { + // Create your large array + auto arr = new double[1_000_000]; + + // Use an index, access every array element by reference (because we're + // going to change each element) and just call parallel on the array! + foreach(i, ref elem; parallel(arr)) { + ref = sqrt(i + 1.0); + } +} +``` |