Inline constructor and InjectFrom calls return Object

Question

Using ValueInjecter, I often find myself writing code like this:

var foo1 = new Foo().InjectFrom(foo2);

But that, unexpectedly, causes foo1 to be of type Object, not Foo. Same with

var foo1 = (new Foo()).InjectFrom(foo2);

and

Foo foo1 = new Foo().InjectFrom(foo2);

won't compile. It's not a big deal, because I can easily do

var foo1 = (Foo)new Foo().InjectFrom(foo2);

or

var foo1 = new Foo();
foo1.InjectFrom(foo2);

and those both work as expected, but I'm curious. Why does the first way not work?

score 4 · Accepted Answer · answered Aug 22 '12 at 12:50

4

I haven't use ValueInjecter, but my suppose is that InjectFrom method returns object value. And as var is sugar syntax, and autodefines variable type during compilation, this variable is defined as Object. That's why you have to use explicit type convertion to make this work for you.

answered Aug 22 '12 at 12:50

Johnny_D

4,592
3
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Of course, I see the difference now. In the first case I'm assigning foo1 the result of the call to InjectFrom(foo2), not the constructor. Thanks, this was a push in the right direction. – wohanley Aug 22 '12 at 13:07

score 1 · Answer 2 · answered Aug 22 '12 at 12:50

1

Try to add custom extension method:

public static T InjectFrom<T>(this T obj, T from) //May be from should be object type
{
    return (T) obj.InjectFrom(foo2);
}

answered Aug 22 '12 at 12:50

Pavel Bakshy

7,697
3
37
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score 1 · Answer 3 · answered Mar 28 '16 at 09:40

1

You could write like this as well:

var foo1 = new Foo().InjectFrom(foo2) as Foo;

answered Mar 28 '16 at 09:40

silkfire

24,585
15
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score 0 · Answer 4 · answered Jun 08 '16 at 18:45

A couple of extensions:

public static class ValueInjecterExtentions
{
    public static T InjectIntoNew<T,TInjection>(this object from) 
        where T: new ()
        where TInjection : Omu.ValueInjecter.Injections.IValueInjection, new()
    {
        return (T) new T().InjectFrom<TInjection>(from);
    }

    public static T InjectIntoNew<T>(this object from)
        where T : new()
    {
        return (T)new T().InjectFrom(from);
    }
}

usage:

var foo = foo2.InjectIntoNew<Foo>();

obviously only usable with default constructor, which is often the case.

Inline constructor and InjectFrom calls return Object

4 Answers4