I'm trying to create some linq expression manually.

At some stage I want to create an expression to concatenate 2 strings, I'm 
trying the following code:

using System.Linq.Expressions;
Expression e1, e2;
return Expression.Call(typeof(string), "Concat", new Type[] { 
typeof(string), typeof(string) }, e1, e2);

this call yield the following error:
System.InvaldOperationExpression
No method 'Concat' on type 'System.String' is compatible with the supplied 
arguments.


Well, well, I'm somewhat surprised...
what else could I try?

Lloyd Dupont <net.galador@ld> wrote:

> I'm trying to create some linq expression manually.
> 
> At some stage I want to create an expression to concatenate 2 strings, I'm 
> trying the following code:
> 
> using System.Linq.Expressions;
> Expression e1, e2;
> return Expression.Call(typeof(string), "Concat", new Type[] { 
> typeof(string), typeof(string) }, e1, e2);
> 
> this call yield the following error:
> System.InvaldOperationExpression
> No method 'Concat' on type 'System.String' is compatible with the supplied 
> arguments.
> 
> 
> Well, well, I'm somewhat surprised...
> what else could I try? 


Your new Type[] ... part is wrong. That means you're trying to call 
string.Concat<string,string>(e1, e2).

Unfortunately, because there are multiple overloads of string.Concat 
which take two parameters, you can't (AFAIK) use this form of 
Expression.Call to create the expression. Instead, use

MethodInfo mi = typeof(string).GetMethod("Concat", 
    new [] {typeof(string), typeof(string) });
return Expression.Call(mi, e1, e2);

-- 
Jon Skeet - 
http://www.pobox.com/~skeet   Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

Thanks Jon!
Looks promising I will give it a try tonight!

As a side note I'm thinking to stop using expression, which are very 
demanding (for example Expression.Add() fail when one expression has an Int 
value and the other and has a Float value) and using the DLR for the same 
purpose.

But Thanks to your tip I can go one step further... I will see...


"Jon Skeet [C# MVP]"  wrote in message

> Your new Type[] ... part is wrong. That means you're trying to call
> string.Concat<string,string>(e1, e2).
>
> Unfortunately, because there are multiple overloads of string.Concat
> which take two parameters, you can't (AFAIK) use this form of
> Expression.Call to create the expression. Instead, use
>
> MethodInfo mi = typeof(string).GetMethod("Concat",
>    new [] {typeof(string), typeof(string) });
> return Expression.Call(mi, e1, e2);