SizeConstructible concept

Description

Vector and matrix objects are charactized by their size. Sometimes it is necessary to create a vector or matrix of the same size (or more mathematically: in the same vector-space) as another vector or matrix. Being able to do this is exactly the purpose of the SizeContructible concept.

Refinement of

Associated types

size_type The size type of the object that allows to construct another object of the same size. The size_type must be Assignable.

Notation

`X`	A type that is a model of SizeConstructible
`x`	Object of type `X`
`n`	object of type convertible to `X::size_type`

Definitions

Valid expressions

Name	Expression	Return type
Size	`x.size()`	`size_type`
Size constructor	`X x(n)`	`X`
Resize [1]	`v.resize(n)`	`void`

Expression semantics

Name	Expression	Semantics	Postcondition
Size	`x.size()`
Size constructor	`X x(n)`	The size-constructor is not the same as the default fill constructor as defined in the Sequence concept. The difference is that the size-constructor is not required to initialise any of the elements. The reason for this is that this initialisation generally takes linear time. And spending this time is generally not necessary because a structure filled with default values is not practical and thus all elements will be seperatly assigned anyway.	`x.size()==n`
Resize [1]	`v.resize(n)`	Resize the vector. The `resize` however does not initialise new elements nor does it garantee that the content will be preserved [2]	`v.size()==n`

Complexity guarantees

Invariants

Notes

[1] The resize member is added because this allows to create for instance a vector of default-constructed vectors. After construction all inner-vector's can be resized to the desired size.

[2]Similar to the size-constructor, the resize member does not default-initialise the elements in the vector. Note that the Sequence concept however does default-initialise new elements during a resize and thus the std::vector does too.