Support C# 9 records

[dgrunwald]

ILSpy should output the short record R(int a, int b); syntax where possible.

Compiler-generated members in records

Example records:

    record R(int A)
    {
        public int B;
        public int C { get; set; }
    }

    record Derived(int X) : R(X * 2);

EqualityContract

Generated unless user-declared.

// R:
protected virtual Type EqualityContract
{
	[CompilerGenerated]
	get
	{
		return typeof(R);
	}
}
// Derived:
protected override Type EqualityContract
{
	[CompilerGenerated]
	get
	{
		return typeof(Derived);
	}
}

Copy Constructor

Generated unless user-declared.

protected R(R original)
{
	b = original.b;
	C = original.C;
}
protected Derived(Derived original)
	: base(original)
{
	X = original.X;
}

Clone method

Always generated; cannot be named in user code.

public virtual R <Clone>$()
{
	return new R(this);
}
public override R <Clone>$()
{
	return new Derived(this);
}

Equals methods

Equals(object?) overload: always generated; error if also user-declared.
Equals(R?) overload: generated unless user-declared.

// R
public override bool Equals(object? obj)
{
	return Equals(obj as R);
}
public virtual bool Equals(R? other)
{
	return (object)other != null && EqualityContract == other.EqualityContract && EqualityComparer<int>.Default.Equals(A, other.A) && EqualityComparer<int>.Default.Equals(B, other.B) && EqualityComparer<int>.Default.Equals(C, other.C);
}
// Derived
public override bool Equals(object? obj)
{
	return Equals(obj as Derived);
}
public sealed override bool Equals(R? other)
{
	return Equals((object?)other);
}
public virtual bool Equals(Derived? other)
{
	return base.Equals(other) && EqualityComparer<int>.Default.Equals(X, other!.X);
}

GetHashCode

Generated unless user-declared.

// R:
public override int GetHashCode()
{
	return ((EqualityComparer<Type>.Default.GetHashCode(EqualityContract) * -1521134295 + EqualityComparer<int>.Default.GetHashCode(A)) * -1521134295 + EqualityComparer<int>.Default.GetHashCode(B)) * -1521134295 + EqualityComparer<int>.Default.GetHashCode(C);
}
// Derived:
public override int GetHashCode()
{
	return base.GetHashCode() * -1521134295 + EqualityComparer<int>.Default.GetHashCode(X);
}

operator==

Always generated; error if also user-declared.

public static bool operator ==(R? r1, R? r2)
{
	return (object)r1 == r2 || (r1?.Equals(r2) ?? false);
}

public static bool operator !=(R? r1, R? r2)
{
	return !(r1 == r2);
}

public static bool operator ==(Derived? r1, Derived? r2)
{
	return (object)r1 == r2 || (r1?.Equals(r2) ?? false);
}

public static bool operator !=(Derived? r1, Derived? r2)
{
	return !(r1 == r2);
}

ToString

Generated if not user-declared.

public override string ToString()
{
	StringBuilder stringBuilder = new StringBuilder();
	stringBuilder.Append("R");
	stringBuilder.Append(" { ");
	if (PrintMembers(stringBuilder))
	{
		stringBuilder.Append(" ");
	}
	stringBuilder.Append("}");
	return stringBuilder.ToString();
}
public override string ToString()
{
	StringBuilder stringBuilder = new StringBuilder();
	stringBuilder.Append("Derived");
	stringBuilder.Append(" { ");
	if (PrintMembers(stringBuilder))
	{
		stringBuilder.Append(" ");
	}
	stringBuilder.Append("}");
	return stringBuilder.ToString();
}

PrintMembers

Generated if not user-declared.

// R:
protected virtual bool PrintMembers(StringBuilder builder)
{
	builder.Append("A");
	builder.Append(" = ");
	builder.Append(A.ToString());
	builder.Append(", ");
	builder.Append("B");
	builder.Append(" = ");
	builder.Append(B.ToString());
	builder.Append(", ");
	builder.Append("C");
	builder.Append(" = ");
	builder.Append(C.ToString());
	return true;
}
// Derived:
protected override bool PrintMembers(StringBuilder builder)
{
	if (base.PrintMembers(builder))
	{
		builder.Append(", ");
	}
	builder.Append("X");
	builder.Append(" = ");
	builder.Append(X.ToString());
	return true;
}

Primary Constructor

Generated only for positional records. Error if also user-declared.

public R(int A)
{
	this.A = A;
	base..ctor();
}
public Derived(int X)
{
	this.X = X;
	base..ctor(X * 2);
}

Deconstruct

Generated only for positional records. Error if also user-declared.

public void Deconstruct(out int A)
{
	A = this.A;
}
public new void Deconstruct(out int X)
{
	X = this.X;
}

[dgrunwald]

For the decompiler this means:

• some members must always be omitted: operator==, operator!=, Equals(object)
• some members can be omitted if equal to the compiler-generated implementation
• the compiler-generated implementation of Equals, GetHashCode and PrintMembers depends on the order of fields/properties.
  • the interleaving of fields and properties is unknown to ILSpy and needs to be inferred from the members
  • Equals/GetHashCode only compares fields and auto-properties; but PrintMembers also prints non-automatic properties.
• primary ctor/deconstruct act on a subset of the properties
  • this subset appears at the start in the list of members being compared

[dgrunwald]

Still missing:

• Primary constructor syntax
• with-expressions
• Tooltips still show class instead of record