EnC Supported Edits

Tomáš Matoušek edited this page Apr 3, 2016 · 10 revisions
Clone this wiki locally

Supported Edits in Edit & Continue (EnC)

Edit & Continue lets you modify/add to your source code in break-mode while debugging without ever having to restart your debugging session.

Definitions

  • Variable Capturing is the mechanism in which the lambda/delegate which is defined inline is able to hold on to any variables within its lexical scope
  • Scope is the region of program text within which it is possible to refer to the entity declared by the name without qualification of the name
  • Debug statement is a span of instructions delimited by subsequent sequence points. Usually a debug statement corresponds to a language statement, but it might correspond to just a part of a language statement (e.g. an opening brace of a block statement), an expression (e.g. lambda body) or other contiguous syntax (base constructor call).
  • Internal active statement is a debug statement that contains a return address of a stack frame.
  • Leaf active debug statement is a debug statement that contains an IP (instruction pointer) of any thread.

Supported Edits

Edit operation Additional Info
Add methods, fields, constructors, properties, events, indexers, field and property initializers, nested types and top-level types (including delegates, enums, interfaces, abstract and generic types, and anonymous types) to an existing type The existing type cannot be a generic or an interface.

Adding or modifying enum members within an existing enum is not supported.
Add and modify iterators Changing a regular method to an iterator method is supported
Add async/await expressions Adding an await expression into an existing async method is not supported.

Adding an await expression around an active statement is not supported.

Changing a regular method to async is supported.
Modify async/await expressions Modifying await expressions wrapped inside other expressions (e.g. G(await F());) is not supported
Add and modify operations with dynamic objects -
Add and modify C# 6.0 language features like string interpolation and null-conditional operators -
Add lambda expressions Lambda expressions can only be added if they are static, access the “this” reference that has already been captured, or access captured variables from a single scope
Modify lambda expressions The following rules guarantee that the structure of the emitted closure tree will not change--thus ensuring that lambdas in the new body are mapped to the corresponding generated CLR methods that implemented their previous versions:
  • Lambda signatures cannot be modified (this includes names, types, ref-ness of parameters, and return types)
  • The set of variables captured by the lambda expression cannot be modified (a variable that has not been captured before cannot be captured after modification and vice versa)
  • The scope of captured variables cannot be modified
  • The set of captured variables accessed by the lambda expression cannot be modified
Add LINQ expressions LINQ expressions contain implicitly-declared anonymous functions. This means the edit rules for lambdas and LINQ will be the same.
Modify LINQ expressions LINQ expressions contain implicitly-declared anonymous functions. This means the edit rules for lambdas and LINQ will be the same.
Modifying async lambda and LINQ expressions in combination You can edit various nested expressions provided that they otherwise satisfy the EnC rules

Not Supported Edits

Edit operation Additional Info
Modify method signatures -
Add or modify generics -
Modify interfaces -
Add a method body such that an abstract method becomes non-abstract -
Add new abstract, virtual, or override member to a type You CAN add a non-abstract member to an abstract type
Add destructor to an existing type -
Modify a type parameter, base type, delegate type, or return type of an event/property/operator/indexer -
Modify a catch-block if it contains an active statement (leaf or internal) -
Modify a try-catch-finally block if the finally clause contains an active statement -
Renaming of any kind -
Delete members, types, namespaces -
Delete entire method bodies Not supported because deleting an entire method body would make the method “abstract”—which is not currently supported
Add using statements -
Add a namespace -
Edit a member referencing an embedded interop type -
Edit a member with On Error or Resume statements Specific to Visual Basic
Edit a member containing an Aggregate, Group By, Simple Join, or Group Join LINQ query clause Specific to Visual Basic
Edit an async method/lambda in a project that doesn't define or reference AsyncStateMachineAttribute type (e.g. projects targeting .NET Framework 4.0 and lower) -
Edit an iterator method/lambda in a project that doesn't define or reference IteratorStateMachineAttribute type (e.g. projects targeting .NET Framework 4.0 and lower) -

App Model EnC Support

Support EnC Do Not Support EnC
  • Apps that support the 4.6 desktop version of the CLR for both x86 and x64 (e.g., Console, WPF, Windows 8.1 apps)
  • UWP in Windows 10
    • ASP.NET 5 apps
    • Silverlight 5
    • Windows Phone 8.1
    • Windows Phone 10
    • Windows Phone emulator scenarios
    • Windows Store 8.1