Maybe< T > 模板类 参考

详细描述

template<typename T>
class shogun::Maybe< T >

Holder that represents an object that can be either present or absent. Quite simllar to std::optional introduced in C++14, but provides a way to pass the reason of absence (e.g. "incorrect parameter").

Essentially, instances are created via

参见

Just or

Nothing

Maybe<int> absent_value = Nothing();
Maybe<int> present_value = Just(3);

To check whether value is present, regular implicit cast to bool is used:

if (maybe_value)
{
    // value exists!
}
else
{
    // value doesn't exist!
}

To obtain value,

参见

value is used:

// may throw an exception
int value = unreliable.value();

To provide default values,

参见

value_or is used:

int value = unreliable.value_or(9);

在文件 maybe.h 第 86 行定义.

Public 成员函数
	Maybe (const Nothing &nothing)
	Maybe (const Maybe< T > &other)
	operator bool () const
T &	value ()
T &	value_or (T &v)
bool	is_absent () const
bool	is_present () const

友元
template<typename Q >
Maybe< Q >	Just (const Q &value)

构造及析构函数说明

Maybe

(

const Nothing &

nothing

)

Creates an instance from nothing resulting in absent value.

参数

nothing

instance of nothing

在文件 maybe.h 第 94 行定义.

Maybe

(

const Maybe< T > &

other

)

Copy constructor.

参数

other

other instance of Maybe for the same type

在文件 maybe.h 第 103 行定义.

成员函数说明

bool is_absent

(

)

const

Returns true if value is absent, false otherwise.

Doesn't throw any exception.

在文件 maybe.h 第 143 行定义.

bool is_present

(

)

const

Returns true if value is present, false otherwise.

Doesn't throw any exception.

在文件 maybe.h 第 152 行定义.

operator bool

(

)

const

Evaluates to true when object is present, false otherwise.

Equivalent to

参见

is_present()

在文件 maybe.h 第 113 行定义.

T& value

(

)

Returns value if it is present, fails otherwise.

异常

ShogunException

if retrieved value is absent

在文件 maybe.h 第 122 行定义.

T& value_or

(

T &

v

)

Returns value if it is present, or the provided default value.

Doesn't throw any exception.

在文件 maybe.h 第 131 行定义.

友元及相关函数文档

Maybe<Q> Just ( const Q &  value )

friend

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该类的文档由以下文件生成:

• maybe.h