Question

You can use Lambda Expression Objects to represent a lambda as an expression.

How do you create a Lambda Expression Object representing a generic method call, if you only know the type -that you use for the generic method signature- at runtime?

For example:

I want to create a Lambda Expression Objects to call:
public static TSource Last<TSource>( this IEnumerable<TSource> source )

But I only know what TSource is at runtime.

Answer 1

static Expression<Func<IEnumerable<T>, T>> CreateLambda<T>()
{
    var source = Expression.Parameter(
        typeof(IEnumerable<T>), "source");

    var call = Expression.Call(
        typeof(Enumerable), "Last", new Type[] { typeof(T) }, source);

    return Expression.Lambda<Func<IEnumerable<T>, T>>(call, source)
}

or

static LambdaExpression CreateLambda(Type type)
{
    var source = Expression.Parameter(
        typeof(IEnumerable<>).MakeGenericType(type), "source");

    var call = Expression.Call(
        typeof(Enumerable), "Last", new Type[] { type }, source);

    return Expression.Lambda(call, source)
}