More Interop Qs (Out, Ref and Structs)


#1

Hi there,

I’ve got a few more questions regarding interop scenarios:

  1. What happens with out parameters in methods? Currently when I try to
    use them I get an error:
    :0: can’t convert String into
    System::Runtime::CompilerServices::StrongBox[System::String] (TypeError)

  2. What happens with ref parameters? it doesn’t throw an error but it
    doesn’t change the value as well.

  3. Structs - they are mapped to Ruby classes, but I can’t create new
    instances of them using the new method. How should it be done?

Thanks and sorry for the question flood :slight_smile:
Shay.

http://www.ironshay.com
Follow me: http://twitter.com/ironshay


#2

Could you be more specific? It’s not helpful if you just say “it doesn’t
work”. Can you include code that you are trying to run and the exact
result you get?

Out parameters are returned in a CLR object array as a return value:

has_value, value = dictionary.try_get_value(“foo”)

Thanks,
Tomas


#3

No problem, here is the list with more details:

  1. out parameters:
    C#

public class Class3 {
public void Test1(out string str) {
str = “From C#”;
}
}

IronRuby

s = “a”
=> “a”

Class3.new.Test1(s)
:0: can’t convert String into
System::Runtime::CompilerServices::StrongBox[System::String] (TypeError)

  1. ref parameters:
    C#

public class Class3 {
public void Test2(ref string str) {
str = “From C#”;
}
}

IronRuby

s = “a”
=> “a”

Class3.new.Test2(s)
=> ‘From C#’

s
=> “a”

(This seems to work like your description to out parameters)

  1. Structs
    C#

public struct FullName {
public string FirstName;
public string LastName;
}

IronRuby

my_struct = FullName.new
:0: allocator undefined for Sample::FullName (TypeError)

Let me know if you need more details.

Many thanks,
Shay

Shay F.
http://www.ironshay.com
Follow me: http://twitter.com/ironshay


#4

[204] > ir
IronRuby 0.5.0.0 on .NET 2.0.50727.4918
Copyright © Microsoft Corporation. All rights reserved.

require ‘temp1’
=> true

Out:

c = Class3.new
=> Class3

a = c.test1
=> ‘From C#’

a
=> ‘From C#’

Ref:

b = c.test2
:0: wrong number of arguments (0 for 1) (ArgumentError)

b = “a”
=> “a”

c.test2 b
=> ‘From C#’

c
=> Class3

b
=> “a”

b = c.test2 b
=> ‘From C#’

b
=> ‘From C#’

I’ll let Tomas explain refs, since I’m not sure what’s going on. It
seems like b = c.test2 should work if b has been defined already, but
that may be just me.
JD

…there is no try


#5

Thanks Jim!

Tomas, do you have an insight about ref params?

Thanks,
Shay.


Shay F.
http://www.ironshay.com
Follow me: http://twitter.com/ironshay


#6

1), 2) ref/out params

C#: bool TryGetValue(string key, out int value)
Ruby call: result, value = dict.try_get_value(‘key’)

I.e. arguments for out parameters are omitted, the values returned via
out parameters are stored in an array returned by the method. The return
value of the method is the first element of that array and is followed
by out and ref parameter return values in the order in which they are
declared.

Another example:
bool Foo(string a, out string b, string c, ref string d, string e, out
string f);

result, b_out, d_out, f_out = foo('a_in ', 'c_in ', ‘d_in’, 'e_in ')

This is a bug. I have a fix for it, so it will work soon.
However, I’d strongly recommend not to use mutable structs. The struct
data are copied when boxed/unboxed and it might not be obvious where
this happens - for example if you pass a struct instance from Ruby to C#
method that accepts it as a strongly typed parameter the struct get
unboxed and its data are copied.

Tomas

IronRuby

s = “a”
=> “a”

Class3.new.Test1(s)
:0: can’t convert String into
System::Runtime::CompilerServices::StrongBox[System::String] (TypeError)


C#


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#7

Thanks so much Tomas!


Shay F.
http://www.ironshay.com
Follow me: http://twitter.com/ironshay