Creating implementation for idiom 306 : Ensure list capacity

Idiom

# 306 Ensure list capacity

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Lead paragraph

Preallocate memory in the list x for a minimum total capacity of 200 elements.

This is not possible in all languages. It is only meant as a performance optimization, should not change the length of x, and should not have any effect on correctness.

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Other implementations

with Ada.Containers.Vectors;

declare
   X : Vector;
begin
   Reserve_Capacity (X, Capacity => 200);
end;

if cap(x) < 200 {
	y := make([]T, len(x), 200)
	copy(y, x)
	x = y
}

Demo

import "slices"

x = slices.Grow(x, 200)

Demo
Doc

import java.util.ArrayList;
import java.util.List;

List<T> x = new ArrayList<>(200);

import java.util.ArrayList;

ArrayList<?> x = new ArrayList<>();
x.ensureCapacity(200);

Uses Classes;

x.capacity := 200;

SetLength(a, 200);

my @list = (undef) x 200;

x.reserve(200);

x := Array new: 200.
"#(nil nil nil nil nil ...)"

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