Class EnumerableToOpt

Facilities for narrowing an existing enumerable to an option value.

Inheritance

Object

EnumerableToOpt

Inherited Members

Object.Equals(Object)

Object.Equals(Object, Object)

Object.GetHashCode()

Object.GetType()

Object.MemberwiseClone()

Object.ReferenceEquals(Object, Object)

Object.ToString()

Namespace: Hgk.Zero.Options.Linq

Assembly: Hgk.Zero.Options.dll

Syntax

public static class EnumerableToOpt

Methods

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WhereElementAt<TSource>(IEnumerable<TSource>, Int32)

Returns an option that contains the element of a sequence at the specified index.

Declaration

public static IOpt<TSource> WhereElementAt<TSource>(this IEnumerable<TSource> source, int index)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	A source sequence.
Int32	index	The zero-based index of the element in source to retrieve.

Returns

Type	Description
IOpt<TSource>	An option containing the element of `source` at the index `index`, or an empty option if index is out of range.

Type Parameters

Name	Description
TSource	The type of the elements of `source`.

Remarks

This method is an option-returning counterpart to ElementAtOrDefault<TSource>(IEnumerable<TSource>, Int32).

This method is implemented using deferred execution; the query represented by this method is not performed until the contents of the returned option are resolved, such as by enumeration.

Exceptions

Type	Condition
ArgumentNullException	`source` is null.

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WhereFirst<TSource>(IEnumerable<TSource>)

Returns an option that contains the first element of a sequence.

Declaration

public static IOpt<TSource> WhereFirst<TSource>(this IEnumerable<TSource> source)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	A source sequence.

Returns

Type	Description
IOpt<TSource>	An option containing the first element of `source`, or an empty option if `source` is empty.

Type Parameters

Name	Description
TSource	The type of the elements of `source`.

Remarks

This method is an option-returning counterpart to FirstOrDefault<TSource>(IEnumerable<TSource>).

This method is implemented using deferred execution; the query represented by this method is not performed until the contents of the returned option are resolved, such as by enumeration.

Exceptions

Type	Condition
ArgumentNullException	`source` is null.

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WhereFirst<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>)

Returns an option that contains the first element of a sequence that satisfies a predicate.

Declaration

public static IOpt<TSource> WhereFirst<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	A source sequence.
Func<TSource, Boolean>	predicate	A function to test elements of `source`.

Returns

Type	Description
IOpt<TSource>	An option containing the first element of `source` that satisfies predicate, or an empty option if no such element exists.

Type Parameters

Name	Description
TSource	The type of the elements of `source`.

Remarks

This method is an option-returning counterpart to FirstOrDefault<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>).

This method is implemented using deferred execution; the query represented by this method is not performed until the contents of the returned option are resolved, such as by enumeration.

Exceptions

Type	Condition
ArgumentNullException	`source` or predicate is null.

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WhereLast<TSource>(IEnumerable<TSource>)

Returns an option that contains the last element of a sequence.

Declaration

public static IOpt<TSource> WhereLast<TSource>(this IEnumerable<TSource> source)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	A source sequence.

Returns

Type	Description
IOpt<TSource>	An option containing the last element of `source`, or an empty option if `source` is empty.

Type Parameters

Name	Description
TSource	The type of the elements of `source`.

Remarks

This method is an option-returning counterpart to LastOrDefault<TSource>(IEnumerable<TSource>).

This method is implemented using deferred execution; the query represented by this method is not performed until the contents of the returned option are resolved, such as by enumeration.

Exceptions

Type	Condition
ArgumentNullException	`source` is null.

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WhereLast<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>)

Returns an option that contains the last element of a sequence that satisfies a predicate.

Declaration

public static IOpt<TSource> WhereLast<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	A source sequence.
Func<TSource, Boolean>	predicate	A function to test elements of `source`.

Returns

Type	Description
IOpt<TSource>	An option containing the last element of `source` that satisfies predicate, or an empty option if no such element exists.

Type Parameters

Name	Description
TSource	The type of the elements of `source`.

Remarks

This method is an option-returning counterpart to LastOrDefault<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>).

This method is implemented using deferred execution; the query represented by this method is not performed until the contents of the returned option are resolved, such as by enumeration.

Exceptions

Type	Condition
ArgumentNullException	`source` or predicate is null.

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WhereSingle<TSource>(IEnumerable<TSource>)

Returns an option that contains the only element of a sequence.

Declaration

public static ISingleResultOpt<TSource> WhereSingle<TSource>(this IEnumerable<TSource> source)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	A source sequence.

Returns

Type	Description
ISingleResultOpt<TSource>	An option containing the only element of `source`, or an empty option if `source` is empty.

Type Parameters

Name	Description
TSource	The type of the elements of `source`.

Remarks

This method is an option-returning counterpart to SingleOrDefault<TSource>(IEnumerable<TSource>).

This method is implemented using deferred execution; the query represented by this method is not performed until the contents of the returned option are resolved, such as by enumeration.

This method returns a single result option ( ISingleResultOpt<T>). If source contains zero elements or one element, this option can be used as an ordinary option ( IOpt<T>). If source contains more than one element, enumerating or resolving this option as an ordinary option will result in an InvalidOperationException being thrown. Methods such as Match<TSource, TResult>(ISingleResultOpt<TSource>, Func<TResult>, Func<TSource, TResult>, Func<TResult>) and ReplaceIfMoreThanOne<TSource>(ISingleResultOpt<TSource>, IOpt<TSource>) can be used to handle the more-than-one case without exceptions.

Exceptions

Type	Condition
ArgumentNullException	`source` is null.
InvalidOperationException	Returned single result was resolved as an ordinary option, but `source` contained more than one element.

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WhereSingle<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>)

Returns an option that contains the only element of a sequence that satisfies an exception.

Declaration

public static ISingleResultOpt<TSource> WhereSingle<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)

Parameters

Type	Name	Description
IEnumerable<TSource>	source	A source sequence.
Func<TSource, Boolean>	predicate	A function to test elements of `source`.

Returns

Type	Description
ISingleResultOpt<TSource>	An option containing the only element of `source` that satisfies `predicate`, or an empty option if there is no such element.

Type Parameters

Name	Description
TSource	The type of the elements of `source`.

Remarks

This method is an option-returning counterpart to SingleOrDefault<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>).

This method is implemented using deferred execution; the query represented by this method is not performed until the contents of the returned option are resolved, such as by enumeration.

This method returns a single result option ( ISingleResultOpt<T>). If source contains zero elements or one element that satisfies predicate, this option can be used as an ordinary option ( IOpt<T>). If source contains more than one element that satisfies predicate, enumerating or resolving this option as an ordinary option will result in an InvalidOperationException being thrown. Methods such as Match<TSource, TResult>(ISingleResultOpt<TSource>, Func<TResult>, Func<TSource, TResult>, Func<TResult>) and ReplaceIfMoreThanOne<TSource>(ISingleResultOpt<TSource>, IOpt<TSource>) can be used to handle the more-than-one case without exceptions.

Exceptions

Type	Condition
ArgumentNullException	`source` or `predicate` is null.
InvalidOperationException	Returned single result was resolved as an ordinary option, but `source` contained more than one element that satisfies `predicate`.