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CSharp Similarities and Differences
This document lists some basic differences between Nemerle and C# in a terse form. If you know Java or C++ it should still be fairly helpful.
Changes In Expressions
| C# | Nemerle | Remarks |
|---|---|---|
const int x = 3;const string y = "foo";readonly Object obj = getObject(); | def x : int = 3;def y : string = "foo";def obj : Object = getObject(); | Variables defined with def cannot be changed once defined. This is similar to readonlyor const in C# orfinal in Java. Most variables in Nemerle aren‘t explicitly typed like this. |
int x = 3;string y = "foo";Object obj = getObject(); | mutable x : int = 3;mutable y : string = "foo";mutable obj : Object = getObject(); | Variables defined with mutable can be changed once defined. Most variables in Nemerle aren‘t explicitly typed like this. |
var = 3; //Will compile.var y; y = "foo";//Won‘t compile. | def = 3;//Will compile!mutable y; y = "foo";//Will compile! | Nemerle‘s type inference is lightyears ahead of C#‘s. If there is clear evidence of a variable‘s type, there‘s a 99% chance Nemerle will infer it. |
int a = b = c; | def a = c;def b = c; | The type of the assignment operator is void. |
value = http://www.mamicode.com/cond ? var1 : var2;> | value = http://www.mamicode.com/if(cond) var1 else var2> | No ternary operator is needed as everything is an expression in Nemerle. The ‘else‘ branch is mandatory here! (Don‘t panic! if-without-else has its own keyword.) |
Class myClass = new Class(parms); | def myClass = Class(parms); | Nemerle doesn‘t require new when calling a constructor. |
Book[] books = new Book[size]; | def books = array(size) : array[Book]; | Often the array type can be inferred and this is simplified; as in the next example. |
Book[] books = new Book[size];books[0] = new Book(); | def books = array(size);books[0] = Book(); | When the type can be inferred from context or later use (which is most of the time), you can drop the type declaration |
int[] numbers = {1, 2, 3}; | def numbers = array[1, 2, 3]; | Initializing an array. Without the arraykeyword this would create a list. |
int[,] numbers = new int[2,3]; | def numbers = array(2,3) : array.[2][int]; | Multidimensional array constructor. The type can usually be inferred from use and not declared. |
int[,] numbers = { {1,2,3}, {1,4,9} }; | def numbers = [ [1,2,3], [1,4,9] ]; | Multidimensional array initialization. |
new {Prop1 = 1; Prop2 = "string"} | using Nemerle.Extensions;new (Prop1 = 1, Prop2 = "string") | Nemerle anonymous typesare a bit more flexible (e. g. can be generic or returned from a method). They must be imported from Nemerle.Extensions however. |
new Class { Property1 = 1; Property2 = "string"} | Class() | The Nemerle Object Modifier macro is more powerful. |
if(cond) answer = 42;... | when(cond) answer = 42;... | if without else is called when. Nemerle requiresif statements to be paired with elsefor clarity. |
if(!cond) answer = 42;... | unless(cond) answer = 42;... | In Nemerle,if(!cond) can use the clearerunless(cond)syntax. Of course,when(!cond) can also always be used. |
if (cond) return foo;do_something ();return bar; | match(cond){ | true => foo| _ => {doSomething(); foo}} | Pattern Matchingprovides a clearer way of delegating control flow. |
if (cond) return foo;do_something ();return bar; | using Nemerle.Imperative;when(cond) return foodo_something ();return bar; | Alternately the Imperative namespace may be imported. This isdiscouragedhowever. |
try {...} catch (FooException e) { ... }catch (BarException e) { ... } | try {...} catch { | e is FooException => ... | e is BarException => ...} | Nemerle‘s somewhat differenttry ... catchsyntax is consistent with its pattern matching syntax. |
(type) expr | expr :> type | Runtime type cast, allows for downcasts and upcasts. |
(type) expr | expr : type | Static cast, only upcasts are allowed. |
using System;using SWF = System.Windows.Forms;using System.Xml;...Console.WriteLine ("foo");SWF.Form x = new SWF.Form();XmlDocument doc = new XmlDocument(); | using System;using System.Console;using SWF = System.Windows.Forms;...WriteLine("foo");def x = SWF.Form();def doc = Xml.XmlDocument(); | In Nemerle, you can apply the usingdirective to classes as well as namespaces. Opened namespaces allow you to drop the prefix of other namespaces, likeSystem inSystem.Xml. More info. |
using System.Windows.Forms;Button button = control as Button;if (button != null) ...else ... | match (control) { | button is Button => ... | listv is ListView => ... | _ => ...//something else} | as can be simulated withmatch. It is a bit more to type up in simple cases, but in general Nemerle‘s construct is more powerful. |
int y = x++;++x; | def y = x;x++;++x; | The ++ and -- operators return void, just like assignment. So, both prefix and postfix versions are equivalent. |
Changes In Type Definitions
| C# | Nemerle | Remarks |
|---|---|---|
static int foo (int x, string y) { ... } | static foo (x : int, y : string) : int { ... } | Types are written after variable names. |
class Foo { public Foo (int x) { ... }} | class Foo { public this (x : int) { ... }} | The constructor‘s name is alwaysthis. |
class Foo { ~Foo () { ... }} | class Foo { protected override Finalize () : void { ... }} | There is no special syntax for the destructor, you just override theFinalizemethod. |
class Foo : Bar { public Foo (int x) : base (x) { ... }} | class Foo : Bar { public this (x : int) { base (x); ... }} | The base constructor is called in the constructor‘s function body. |
class Foo { int x;} | class Foo { mutable x : int;} | Fields which will be changed outside of the constructor need to be marked asmutable. |
class Foo { readonly int x; const int y = 10;} | class Foo { x : int; y : int = 10;} | Read-only/const are used by default. |
class Foo { static int x = 1;} | class Foo { static mutable x : int = 1;} | Static variable. |
class Foo { static readonly int x; static int method() { ... } } | module Foo { x : int; method() : int { ... } } | A module is a class in which all members are static. |
using System.Runtime.CompilerServices.CSharp;class C { public object this [int i] { ... } [IndexerName("MyItem")] public int this [string name] { ... }} | class C { public Item [i : int] : object { ... } public MyItem [name : string] : int { ... }} | Indexers. |
| C# | Nemerle |
|---|---|
| When two interfaces use the same method to perform different functions, different names can be given to each method. | |
interface SpeaksEnglish{ void Speak();}interface SpeaksGerman{ void Speak();}class GermanTransfer : SpeaksEnglish, SpeaksGerman{ public void SpeaksEnglish.Speak() {} public void SpeaksGerman.Speak() {}} | interface SpeaksEnglish{ Speak() : void;}interface SpeaksGerman{ Speak() : void;}class GermanTransfer : SpeaksEnglish, SpeaksGerman{ public Speak() : void implements SpeaksEnglish.Speak{} public Sprechen() : void implements SpeaksGerman.Speak{}} |
Generics
| C# | Nemerle | Remarks |
|---|---|---|
class A { T x; } | class A [T] { x : T; } | Type parameters are written in square brackets [...]. |
typeof(A); | typeof(A[_,_]); | typeof expression |
New Stuff
Nemerle contains many constructs which are not present in C#. Unfortunately, most of them don‘t really fit into a side-by-side comparison format:
- Tuples -- a nameless, heterogeneous data structure.
- Lists -- a special syntax for lists and list processing.
- The Void Literal -- a useful construct for recursive functions.
- Local functions -- defining functions within other functions.
- Functional Values -- passing functions as arguments and returning them from other functions.
- Anonymous Functions -- defining functions which don‘t need names.
- Variants and Pattern Matching -- an alternative, and very useful, control flow construct.
- Macros -- writing code that writes code.
Other Minor Differences
Ambiguity Isn‘t Tolerated
namespace YourAttributes{ class Serializable : System.Attribute { }}namespace MyAttributes{ using YourAttributes; class Serializable : System.Attribute { } [Serializable] class SomeClass { }}C# compilers will choose MyAttributes.Serializable or, if its definition is commented out, YourAttributes.Serializable. Nemerle will raise an error telling you to be more specific about which attribute you want to use.
Exclusion of Overridden Methods
class BaseClass { public virtual AddItem (val : string) : void { } } class TestClass : BaseClass { public AddItem (val : object) : void { } public override AddItem (val : string) : void { } } ... TestClass().AddItem ("a"); // C# will choose TestClass.AddItem (object) // Nemerle will choose TestClass.AddItem (string)This behaviour comes from section 7.6.5.1 of the C# specification, which states "...methods in a base class are not candidates [for overload resolution] if any method in a derived class is applicable (§7.6.5.1)." Unfortunately, this rule is patently absurd in situations like the above. The Nemerle compiler always chooses the method whose signature best matches the given arguments.
CSharp Similarities and Differences
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