An unnecessary string is created through a call to System.String.ToLower or System.String.ToUpper.

A System.String object is immutable. Any change to a string requires creating a new String object. Unnecessary string creation degrades performance. This rule flags the following operations that create unnecessary strings:

1. Multiple calls to ToLower, ToLowerInvariant, ToUpper, or ToUpperInvariant on the same string instance.

2. Calling System.String.Equals, System.String.op_Equality(System.String,System.String), or System.String.op_Inequality(System.String,System.String) on a string created by calling ToLower or ToUpper.

3. Passing a string created by calling ToLower or ToUpper to a member of System.Collections.Specialized.HybridDictionary.

To fix a violation of this rule eliminate the unnecessary string creation by removing the call to ToLower or ToUpper. The following fixes correspond to the numbering in the Description section:

1. Assign the result of the first ToLower or ToUpper call to a new variable and use this variable instead of the remaining calls.

2. Replace the call to Equals, op_Equality, or op_Inequality with a case-insensitive call to System.String.Compare.

3. Use a case-insensitive HybridDictionary, which is created by passing true as the caseInsensitive argument to the constructor.

It is safe to exclude a warning from this rule; however, performance might suffer.

Do not concatenate strings inside loops

Test for empty strings using string length