ExpressionToCode

ExpressionToCode generates valid, readable C# from an Expression Tree. (nuget: ExpressionToCodeLib)

An example:

  ExpressionToCode.ToCode(
    () => new[] { 1.0, 2.01, 3.5 }.SequenceEqual(new[] { 1.0, 2.01, 3.5 })
  )
== "() => new[] { 1.0, 2.01, 3.5 }.SequenceEqual(new[] { 1.0, 2.01, 3.5 })"

ExpressionToCode also provides something like Groovy's Power Assert which includes the code of the failing assertion's expression and the values of its subexpressions. This functionality is particularly useful in a unit testing framework such as NUnit or xUnit.NET. When you execute the following (failing) assertion:

PAssert.That(()=>Enumerable.Range(0,1000).ToDictionary(i=>"n"+i)["n3"].ToString()==(3.5).ToString());

The assertion fails with the following message:

assertion failed

Enumerable.Range(0, 1000).ToDictionary(i => "n" + i)["n3"].ToString(CultureInfo.InvariantCulture) == 3.5.ToString(CultureInfo.InvariantCulture)
   →   false (caused assertion failure)

Enumerable.Range(0, 1000).ToDictionary(i => "n" + i)["n3"].ToString(CultureInfo.InvariantCulture)
     →   "3"

Enumerable.Range(0, 1000).ToDictionary(i => "n" + i)["n3"]
     →   3

Enumerable.Range(0, 1000).ToDictionary(i => "n" + i)
     →   new Dictionary<string, int> {
              ["n0"] = 0,
              ["n1"] = 1,
              ["n2"] = 2,
              ["n3"] = 3,
              ["n4"] = 4,
              ["n5"] = 5,
              ["n6"] = 6,
              ["n7"] = 7,
              ["n8"] = 8,
              ["n9"] = 9,
              ["n10"] = 10,
              ["n11"] = 11,
              ["n12"] = 12,
              ["n13"] = 13,
              ["n14"] = 14,
              ["n15"] = 15,
              ["n16"] = 16,
              ["n17"] = 17,
              ["n18"] = 18,
              ["n19"] = 19,
              ["n20"] = 20,
              ["n21"] = 21,
              ["n22"] = 22,
              ["n23"] = 23,
              ["n24"] = 24,
              ["n25"] = 25,
              ["n26"] = 26,
              ["n27"] = 27,
              ["n28"] = 28,
              ["n29"] = 29,
              ...
          }

Enumerable.Range(0, 1000)
     →   { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, ... }

3.5.ToString(CultureInfo.InvariantCulture)
     →   "3.5"

ExpressionToCode's output is configurable in various ways. For expressions with small values, a values-on-stalks rendering might instead be used:

var a = 2;
var b = 5;
ExpressionToCodeConfiguration.DefaultAssertionConfiguration.WithAnnotator(CodeAnnotators.ValuesOnStalksCodeAnnotator)
    .Assert(() => Math.Max(a, b) > new[] { 3, 8, 13, 4 }.Average() );

Math.Max(a, b) > new[] { 3, 8, 13, 4 }.Average()  :  assertion failed
      │  │  │       │                     │
      │  │  │       │                     7.0
      │  │  │       new[] { 3, 8, 13, 4 }
      │  │  5
      │  2
      5

Note that the default configuration for asserts (i.e. PAssert.That) limits the length of sequences and strings; the default configuration of code-generation does not.

ExpressionToCode was inspired by Power Assert.NET. It differs from PowerAssert.NET by supporting a larger portion of the lambda syntax and that the generated C# is more frequently valid; the aim is to generate valid C# for all expression trees created from lambda's. Currently supported:

Expression tree support

Supports static field and property access
Supports more operators, e.g. logical and bitwise negation
Recognizes C# indexer use (e.g. dict["mykey"]==3), in addition to special cases for array indexers and string indexers
Adds parentheses where required by operator precedence and associativity (e.g. () => x - (a - b) + x * (a + b) is correctly regenerated)
Generates valid numeric and other constant literals including escapes and suffixes where required (e.g. 1m + (decimal)Math.Sqrt(1.41))
Supports C# syntactic sugar for object initializers, object member initializers, list initializers, extension methods, anonymous types (issues #12, #3), etc
Uses the same spacing rules Visual Studio does by default
Supports nested Lambdas
Expands generic type instances and nullable types into normal C# (e.g. Func<int, bool> and int?)
Recognizes references to this and omits the keyword where possible (#5)
Recognizes closed-over variables and prints something plausible, rather than the crypic compiler-generated names.
Omits most implicit casts (e.g. object.Equals(3, 4) instead of object.Equals((object)3, (object)4)) - user defined implicit cast operators are not elided (#4)
Detects when type parameters to methods are superfluous (#13).

Not implemented (yet?):

Use LINQ query syntax where possible - issue #6.
Explicitly cast otherwise inferable lambda when required due to ambiguous overloads - issue #14.
Warn when == differs from .Equals or .SequenceEquals, as Power Assert.NET does (issue #2).
See all open issues.