Change
Add Peek() method to ThreadContextStack and LogicalThreadContextStack to be able to get the most recent value from the context without removing it.

Motivation
In the scope of ElasticCommonSchema .NET integration for log4net log entry properties are being read and written to ECS format. In case of context stacks current implementation takes string representation of the stack. It works fine when stack (i.e., property) has a single value, but there are also cases when stack contains multiple values (same or different ones). With the proposed changes it will be able to take the most recent value, in the context of which the current log entry is being written.

Consider following scenario:

using
 (
LogicalThreadContext
.
Stacks
[
"
Id
"
]
.
Push
(
"
123
"
)
)

{

    log
.
Info
(
"
Log 1
"
)
;
 // currently has "123" in the log metadata


    using
 (
LogicalThreadContext
.
Stacks
[
"
Id
"
]
.
Push
(
"
456
"
)
)

    {

        log
.
Info
(
"
Log 2
"
)
;
 // currently has "123 456" in the log metadata; should have "456" instead


        using
 (
LogicalThreadContext
.
Stacks
[
"
Id
"
]
.
Push
(
"
789
"
)
)

        {

            log
.
Info
(
"
Log 3
"
)
;
 // currently has "123 456 789" in the log metadata; should have "789" instead

        }

    }

}

Alternative solutions considered
An alternative approach might be to just pop the most recent value and then push it again onto the stack. Problem here is that it creates a new scope which will not be closed as no one will call Dispose() on the returned result from Push() .