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RCS1227: Validate arguments correctly

Properties​

PropertyValue
Default SeverityInfo
Minimum language version-

Summary​

  An iterator method (a method that contains `yield`) will not validate arguments until the caller begins to enumerate the result items.

  To ensure that arguments are validated immediately (when the method is called), move
  the iterator to a separate method (local function).

Examples​

Example #1​

diagnostic.cs
IEnumerable<object> Foo(IEnumerable<object> items)
{
    if (items == null)
        throw new ArgumentNullException(nameof(items));

    foreach (object item in items)
        yield return item;
}
fix.cs
IEnumerable<object> Foo(IEnumerable<object> items)
{
    if (items == null)
        throw new ArgumentNullException(nameof(items));

    return FooIterator();

    IEnumerable<object> FooIterator()
    {
        foreach (object item in items)
            yield return item;    
    }
}

Applies to​