Indexer (programming): Difference between revisions

Revision as of 04:44, 9 January 2025

Revision as of 15:52, 11 January 2025

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In C++ one can emulate indexing by overloading the {{c++|[]}} operator. The expression {{c++|a[b...]}} translates to a call to the user-defined function {{c++|operator[]}} as {{c++|(a).operator[](b...)}}.<ref>{{cite web|url=https://en.cppreference.com/w/cpp/language/operators|title=C++ operator overloading}}</ref> Here is an example,

<syntaxhighlight lang="c++">

struct vector {

int size; double* data;

vector(int n) { size = n; data = new double[n](); }

~vector(){ size = 0; delete[] data; }

double& operator[](int i) { return data[i]; }

};

#include<iostream>

int main() {

vector v(3);

for(int i = 0; i < v.size; i++) v[i] = i + 1;

for(int i = 0; i < v.size; i++) std::cout << v[i] << "\n";

return 0;

}

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==== Example 1====

<syntaxhighlight lang="csharp">

public class vectorVector
{

private double[] data;

public vectorVector(int n) { data = new double[n]; }

public int size => data.Length;

public double this[int i] { get => data[i]; set => data[i] = value; }

public static void Main(){

} {

var v=new vector(3);

for(int i=0;i<v.size;i++) var v[i] =i+1 new Vector(3);

for (int i = 0; i < v.size; i++) System.Console.WriteLine(v[i]) = i + 1;

for (int i = 0; i < v.size; i++) System.Console.WriteLine(v[i]);

}

}

}

</syntaxhighlight>

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=== PHP ===

In [[PHP]] indexing can be implemented via the predefined {{pythoncode|ArrayAccess}} interface,<ref>{{cite web|url=https://www.php.net/manual/en/class.arrayaccess.php|title=PHP ArrayAccess interface}}</ref>

<syntaxhighlight lang="php">

<?php

class vectorVector implements ArrayAccess {

function __construct(int $n) {

$this->size = $n;

$this->data = array_fill(0, $n, 0);

}

public function offsetGet($offset): mixed {

return $this->data[$offset];

}

public function offsetSet($offset, $value): void {

$this->data[$offset] = $value;

}

public function offsetExists($offset): bool {}

public function offsetUnset($offset): void {}

}

$v = new vectorVector(3);

for ($i = 0; $i < $v->size; $i++) $v[$i] = $i + 1;

for ($i = 0; $i < $v->size; $i++) print "{$v[$i]}\n";

?>

</syntaxhighlight>

=== Python ===

In [[Python (programming language)|Python]] one implements indexing by overloading the {{python|__getitem__}} and {{python|__setitem__}} methods,

<syntaxhighlight lang="python">

import array

class vector Vector(object) :

def __init__ (self, n) :

self.size = n

self.data = array.array('"d'", [0.0] * n)

def __getitem__ (self, i) : return self.data[i]

def __setitem__ (self, i, value) : self.data[i] = value

v = Vector(3)

for i in range(v.size) : v[i] = i + 1

for i in range(v.size) : print(v[i])

</syntaxhighlight>

=== Rust ===

[[Rust (programming language)|Rust]] provides the {{Mono|std::ops::Index}} trait.<ref>{{cite web |title=Index in std::ops - Rust |url=https://doc.rust-lang.org/std/ops/trait.Index.html |website=doc.rust-lang.org |access-date=11 January 2025}}</ref>

<syntaxhighlight lang="rust">

use std::ops::Index;

enum Nucleotide {

A,

C,

G,

T,

}

struct NucleotideCount {

a: usize,

c: usize,

g: usize,

t: usize,

}

impl Index<Nucleotide> for NucleotideCount {

type Output = usize;

fn index(&self, nucleotide: Nucleotide) -> &Self::Output {

match nucleotide {

Nucleotide::A => &self.a,

Nucleotide::C => &self.c,

Nucleotide::G => &self.g,

Nucleotide::T => &self.t,

}

}

}

let nucleotide_count = NucleotideCount {a: 14, c: 9, g: 10, t: 12};

v=vector(3)

assert_eq!(nucleotide_count[Nucleotide::A], 14);

for i in range(v.size) : v[i]=i+1

assert_eq!(nucleotide_count[Nucleotide::C], 9);

for i in range(v.size) : print(v[i])

assert_eq!(nucleotide_count[Nucleotide::G], 10);

assert_eq!(nucleotide_count[Nucleotide::T], 12);

</syntaxhighlight>

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{{Reflist}}

[[Category:Articles with example C++ code]]

<!--Categories-->

[[Category:Articles with example C Sharp code]]

[[Category:Articles with example Python (programming language) code]]

[[Category:Articles with example PHP code]]

[[Category:Articles with example Rust code]]

[[Category:Programming language topics]]

[[Category:Object-oriented programming]]