[Ironruby-core] Comparing CLR strings and Ruby strings - a slightly surprising behaviour

Tomas Matousek Tomas.Matousek at microsoft.com
Tue Mar 3 18:24:23 EST 2009


We don't plan to make the highlighted code work. However we are going to make this work:

string s = engine.Execute<string>("'hi'")

and also this works:

string s = engine.Execute("'hi'").ToString(),

although in this case you need to take care of null.

The difference is that unlike Execute, Execute<T> invokes an explicit dynamic conversion on the resulting type. You can achieve the same using engine.ObjectOperations.ConvertTo<string>(engine.Execute("'hi'")).

Tomas

From: ironruby-core-bounces at rubyforge.org [mailto:ironruby-core-bounces at rubyforge.org] On Behalf Of Meinrad Recheis
Sent: Tuesday, March 03, 2009 2:19 PM
To: ironruby-core at rubyforge.org
Subject: Re: [Ironruby-core] Comparing CLR strings and Ruby strings - a slightly surprising behaviour

On Tue, Mar 3, 2009 at 11:11 PM, Meinrad Recheis <meinrad.recheis at gmail.com<mailto:meinrad.recheis at gmail.com>> wrote:
On Tue, Mar 3, 2009 at 9:46 PM, Thibaut Barrère <thibaut.barrere at gmail.com<mailto:thibaut.barrere at gmail.com>> wrote:
Hi,

while writing specs for Magic, I noticed that:
instance_from(MenuItem, "Hello").text.to_s.should == "Hello"

to_s is required to get the assertion to pass. The following will return false:

button = Button.new
button.text = "Hello"
puts button.text == "Hello"

So I guess that CLR strings cannot be compared to Ruby strings unless to_s is applied.

I have stumbled on this too and was very surprised. This problem does not exist in IronPython (does it? please correct me if I am wrong). The behavior I was expecting is that "on the ruby" side all strings are (or at least behave exactly like) ruby strings, even if they come from .NET and are automatically converted to clr-strings when passed into clr methods.

In addition to that, it would also be great to have automatic type conversion on the .NET side too. I'd expect to be able to assign a string pulled out from the interpreter to a C# string without the need to call ToString(). For example,

string s = engine.Execute("'hi'") as string;

Currently s would be null because the dynamic cast to System.String fails.
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