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digitalmars.D.learn - Why Throwable.message is not a property

reply uranuz <neuranuz gmail.com> writes:
The question is why Throwable.message is not a  property?! It 
looks strange now, because "message" is not a *verb*, but a 
*noun*. So it's expected to be a property. Also because it is not 
a property in some contexts when I try to concatenate it with 
string without parentheses using "~" operator it fails, because 
(as you could expect) it is a *regular* function, but not a 
property.

I wonder if it was made as *non-property* by some reason or by 
oversight?

Thanks
Mar 17 2021
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Wednesday, 17 March 2021 at 17:46:27 UTC, uranuz wrote:

 Also because it is not a property in some contexts when I try 
 to concatenate it with string without parentheses using "~" 
 operator it fails


Can you post some sample code that demonstrates this?
Mar 17 2021
parent reply uranuz <neuranuz gmail.com> writes:
On Wednesday, 17 March 2021 at 17:52:20 UTC, Adam D. Ruppe wrote:

 On Wednesday, 17 March 2021 at 17:46:27 UTC, uranuz wrote:

 Also because it is not a property in some contexts when I try 
 to concatenate it with string without parentheses using "~" 
 operator it fails


 Can you post some sample code that demonstrates this?


Seems that a problem with concatenation is because 
Throwable.message has const(char)[] type, but not string. This 
makes some inconvenience ;-)

There is an example:

import std;

void main()
{
     auto exc = new Exception("Test");
     string longMsg = "The: " ~ exc.message; // Adding parentheses 
() after "message" actually doesn't change anything. Error is the 
same
     writeln(longMsg);
}

Compile error:

onlineapp.d(6): Error: cannot implicitly convert expression "The: 
" ~ exc.message() of type char[] to string

I could add cast(string), but it's not something I want to do.

The reason, why I want to use "message" instead of "msg" is that 
I want to add some extra information to exception as separate 
typed fields. But I want it to be displayed when converting 
exception to string. So I shall override "message" and convert 
this extra info to string...
Mar 17 2021
parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Wednesday, 17 March 2021 at 19:32:02 UTC, uranuz wrote:

 Seems that a problem with concatenation is because 
 Throwable.message has const(char)[] type, but not string. This 
 makes some inconvenience ;-)


Yes, that's what I thought.

The concat operation tends to give the most flexible type of the 
arguments... and I wish it would then ACTUALLY use that 
flexibility... but it doesn't.

Regardless though since you know you are concating it, which 
means you get a new string anyway, you can safely cast(string) it.

string longMsg = "The: " ~ cast(string) exc.message;

that's how i do it.
Mar 17 2021
parent uranuz <neuranuz gmail.com> writes:
On Wednesday, 17 March 2021 at 19:38:48 UTC, Adam D. Ruppe wrote:

 On Wednesday, 17 March 2021 at 19:32:02 UTC, uranuz wrote:

 Seems that a problem with concatenation is because 
 Throwable.message has const(char)[] type, but not string. This 
 makes some inconvenience ;-)


 Yes, that's what I thought.

 The concat operation tends to give the most flexible type of 
 the arguments... and I wish it would then ACTUALLY use that 
 flexibility... but it doesn't.

 Regardless though since you know you are concating it, which 
 means you get a new string anyway, you can safely cast(string) 
 it.

 string longMsg = "The: " ~ cast(string) exc.message;

 that's how i do it.


This is what I have done ;-)
Mar 17 2021