These are undocumented implementation details of the compiler, and subject to change at any time. (UPDATE: See GeneratedNames.cs
in the C# sources for the current details; the description below is somewhat out-of-date.)
However, since I’m a nice guy, here are some of those details:
If you have an unused local variable that the optimizer removes, we emit debug info for it anyway into the PDB. We stuck the suffix __Deleted$ onto such variables so that the debugger knows that they were in source code but not represented in the binary.
Temporary variable slots allocated by the compiler are given names with the pattern CS$X$Y, where X is the “temporary kind” and Y is the number of temporaries allocated so far. The temporary kinds are:
0 --> short lived temporaries
1 --> return value temporaries
2 --> temporaries generated for lock statements
3 --> temporaries generated for using statements
4 --> durable temporaries
5 --> the result of get enumerator in a foreach
6 --> the array storage in a foreach
7 --> the array index storage in a foreach.
Temporary kinds between 8 and 264 are additional array index storages for multidimensional arrays.
Temporary kinds above 264 are used for temporaries involving the fixed statement fixing a string.
Special compiler-generated names are generated for:
1 --> the iterator state ("state")
2 --> the value of current in an iterator ("current")
3 --> a saved parameter in an iterator
4 --> a hoisted 'this' in an iterator ("this")
5 --> a hoisted local in an iterator
6 --> the hoisted locals from an outer scope
7 --> a hoisted wrapped value ("wrap")
8 --> the closure class instance ("locals")
9 --> the cached delegate instance ("CachedAnonymousMethodDelegate")
a --> the iterator instance ("iterator")
b --> an anonymous method
c --> anonymous method closure class ("DisplayClass")
d --> iterator class
e --> fixed buffer struct ("FixedBuffer")
f --> anonymous type ("AnonymousType")
g --> initializer local ("initLocal")
h --> query expression temporary ("TransparentIdentifier")
i --> anonymous type field ("Field")
j --> anonymous type type parameter ("TPar")
k --> auto prop field ("BackingField")
l --> iterator thread id
m --> iterator finally ("Finally")
n --> fabricated method ("FabricatedMethod")
o --> dynamic container class ("SiteContainer")
p --> dynamic call site ("Site")
q --> dynamic delegate ("SiteDelegate")
r --> com ref call local ("ComRefCallLocal")
s --> lock taken local ("LockTaken")
The pattern for generating magical names is: P<N>C__SI where:
- P is CS$ for cached delegates and display class instances, empty otherwise.
- N is the original name associated with the thing, if any
- C is the character 1 through s listed above
- S is a descriptive suffix (“current”, “state”, and so on) so that you don’t have to have the table above memorized when reading the metadata.
- I is an optional unique number