Requirements: To define a collection, we need to get the last element of the collection, the code is usually array[array. Length - 1] In this way, C# 8.0 introduces a new index expression meaning "from the last". The feature will introduce a new unary prefix "hat" operator.
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System index
C# can't index a collection from the end, but most indexers use the concept of "start with", or execute the "length-i" expression. We introduced a new index expression that means "from the end". The feature will introduce a new unary prefix "hat" operator. Its single operand must be convertible to System.Int32. It will be reduced to the appropriate System.Index factory method call.
string[] words = new string[]
{
// index from start index from end
"The", // 0 ^9
"quick", // 1 ^8
"brown", // 2 ^7
"fox", // 3 ^6
"jumps", // 4 ^5
"over", // 5 ^4
"the", // 6 ^3
"lazy", // 7 ^2
"dog" // 8 ^1
}; // 9 (or words. Length) ^0
The index is the same as 0 sequence[0]. The index is the same as ^0 sequence[sequence. Length]。 The expression sequence[^0] does throw an exception, just like sequence[sequence. Length]. For any number n, the index ^n is the samesequence. Length - n。
Unhandled exception. System.IndexOutOfRangeException: Index was outside the bounds of the array.
Resources:
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