internal static object ComparisonValueFromExpression(this Expression expression, out Type type, out bool cachable)
{
type = null;
cachable = false;
if (expression == null)
{
return(null);
}
switch (expression)
{
case LambdaExpression lambdaExpression:
type = lambdaExpression.Parameters.FirstOrDefault()?.Type;
break;
case MemberExpression memberExpression:
type = memberExpression.Member.DeclaringType;
break;
case MethodCallExpression methodCallExpression:
// special case F# method call expressions on FuncConvert
// that are used to convert F# quotations representing lambda expressions, to expressions.
// https://github.com/dotnet/fsharp/blob/7adaacf150dd79f072efe42d43168c9cd6edbced/src/fsharp/FSharp.Core/Linq.fs#L796
//
// For example:
//
// type Doc = { Message: string; State: string }
// let field (f:Expr<'a -> 'b>) =
// Microsoft.FSharp.Linq.RuntimeHelpers.LeafExpressionConverter.QuotationToExpression f
// |> Nest.Field.op_Implicit
//
// let fieldExpression = field <@ fun (d: Doc) -> d.Message @>
//
if (methodCallExpression.Method.DeclaringType.FullName == "Microsoft.FSharp.Core.FuncConvert" &&
methodCallExpression.Arguments.FirstOrDefault() is LambdaExpression lambda)
{
type = lambda.Parameters.FirstOrDefault()?.Type;
}
else
{
throw new Exception($"Unsupported {nameof(MethodCallExpression)}: {expression}");
}
break;
default:
throw new Exception(
$"Expected {nameof(LambdaExpression)}, {nameof(MemberExpression)} or "
+ $"{nameof(MethodCallExpression)}, received: {expression.GetType().Name}");
}
var visitor = new ToStringExpressionVisitor();
var toString = visitor.Resolve(expression);
cachable = visitor.Cachable;
return(toString);
}
internal static object ComparisonValueFromExpression(this Expression expression, out Type type, out bool cachable)
{
type = null;
cachable = false;
if (expression == null)
{
return(null);
}
if (!(expression is LambdaExpression lambda))
{
throw new Exception($"Not a lambda expression: {expression}");
}
type = lambda.Parameters.FirstOrDefault()?.Type;
var visitor = new ToStringExpressionVisitor();
var toString = visitor.Resolve(expression);
cachable = visitor.Cachable;
return(toString);
}