Styjun

Half-rock- half-forest-gnome

Our group keeps dying during the Lost Mine of Phandelver campaign. What are we doing wrong?

Is it double speak?

If there were no space agencies, could a person go to space?

In Pokémon Go, why does one of my Pikachu have an option to evolve, but another one doesn't?

What is the resistivity of copper at 3 kelvin?

Can we use other things than single-word verbs in our dialog tags?

Does bottle color affect mold growth?

Need help understanding lens reach

How does The Fools Guild make its money?

Does this smartphone photo show Mars just below the Sun?

I was contacted by a private bank overseas to get my inheritance

"How do you solve a problem like Maria?"

Double blind peer review when paper cites author's GitHub repo for code

Short story about a teenager who has his brain replaced with a microchip (Psychological Horror)

Why is there a need to prevent a racist, sexist, or otherwise bigoted vendor from discriminating who they sell to?

How quickly could a country build a tall concrete wall around a city?

Traveling from Germany to other countries by train?

sytemctl status log output

Whats the name of this projection?

How does the oscilloscope trigger really work?

Is there a loss of quality when converting RGB to HEX?

Why do private jets such as Gulfstream fly higher than other civilian jets?

Did WWII Japanese soldiers engage in cannibalism of their enemies?

A field of “channel” type gives error “Cannot default-initialize a variable with generic type”

Good practice to hold a file or channel in a classHow do I use generics with an array of Classes?ReSharper warns: “Static field in generic type”How to create object that can be added to a List<T> array?How can I make different captures of a wildcard compatible?Initializing a Generic variable from a C# Type VariableSwift generics not preserving typeGeneric Table ModelHow to solve “no generic parameters allowed”Swift generic subclass of regular class “cannot convert value of type to expected argument type”swift convenience init and generic class

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

4

In this code, I am creating a class that contains a channel that may be opened upon request when initialized. To do so, I am passing a flag to indicate whether a channel is opened or not (together with its file name).

class Myclass

 var writeflag : bool;
 var output : channel;

 proc init( writeflag = false, filename = "" )
 
 this.writeflag = writeflag;
 if writeflag // (1)
 assert( filename != "" );
 this.output = openwriter( filename );
 // (2)
 


proc main()

 var a = new owned Myclass( writeflag = true,
 filename = "test.out" );
 a.output.writeln( 123 );

However, the compiler rejects the above code with the message:

myclass.chpl:6: error: Cannot default-initialize a variable with generic type
myclass.chpl:6: note: 'not-fully-instantiated' has generic type 'channel'

On the other hand, if I comment out (1) and (2), the code works as expected and creates "test.out". I guess the problem is related to the generic nature of channel (according to the error message), but not very sure how to write such a code appropriately...

file generics chapel

share|improve this question

asked Mar 27 at 5:59

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  channel.isclosed() might be helpful for your application, in case you weren't aware of it.
  
  – bencray
  Mar 27 at 13:40
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You don't get the error when the if statement is commented out because the lack of an else branch is what is triggering the error message. Basically, the Chapel compiler knows the type for output when you assign to it, but if the if statement isn't triggered, it doesn't know what default value to give it (hence bencray's recommendation).
  
  – Lydia Duncan
  Mar 27 at 15:23
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I see... I think it explains the behavior of the above code, and why such an error did not occur in my previous code. Thanks very much :-)
  
  – roygvib
  Mar 27 at 15:32
  
  

  
  
  
  

add a comment | 

4

In this code, I am creating a class that contains a channel that may be opened upon request when initialized. To do so, I am passing a flag to indicate whether a channel is opened or not (together with its file name).

class Myclass

 var writeflag : bool;
 var output : channel;

 proc init( writeflag = false, filename = "" )
 
 this.writeflag = writeflag;
 if writeflag // (1)
 assert( filename != "" );
 this.output = openwriter( filename );
 // (2)
 


proc main()

 var a = new owned Myclass( writeflag = true,
 filename = "test.out" );
 a.output.writeln( 123 );

However, the compiler rejects the above code with the message:

myclass.chpl:6: error: Cannot default-initialize a variable with generic type
myclass.chpl:6: note: 'not-fully-instantiated' has generic type 'channel'

On the other hand, if I comment out (1) and (2), the code works as expected and creates "test.out". I guess the problem is related to the generic nature of channel (according to the error message), but not very sure how to write such a code appropriately...

file generics chapel

share|improve this question

asked Mar 27 at 5:59

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  channel.isclosed() might be helpful for your application, in case you weren't aware of it.
  
  – bencray
  Mar 27 at 13:40
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You don't get the error when the if statement is commented out because the lack of an else branch is what is triggering the error message. Basically, the Chapel compiler knows the type for output when you assign to it, but if the if statement isn't triggered, it doesn't know what default value to give it (hence bencray's recommendation).
  
  – Lydia Duncan
  Mar 27 at 15:23
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I see... I think it explains the behavior of the above code, and why such an error did not occur in my previous code. Thanks very much :-)
  
  – roygvib
  Mar 27 at 15:32
  
  

  
  
  
  

add a comment | 

In this code, I am creating a class that contains a channel that may be opened upon request when initialized. To do so, I am passing a flag to indicate whether a channel is opened or not (together with its file name).

class Myclass

 var writeflag : bool;
 var output : channel;

 proc init( writeflag = false, filename = "" )
 
 this.writeflag = writeflag;
 if writeflag // (1)
 assert( filename != "" );
 this.output = openwriter( filename );
 // (2)
 


proc main()

 var a = new owned Myclass( writeflag = true,
 filename = "test.out" );
 a.output.writeln( 123 );

However, the compiler rejects the above code with the message:

myclass.chpl:6: error: Cannot default-initialize a variable with generic type
myclass.chpl:6: note: 'not-fully-instantiated' has generic type 'channel'

On the other hand, if I comment out (1) and (2), the code works as expected and creates "test.out". I guess the problem is related to the generic nature of channel (according to the error message), but not very sure how to write such a code appropriately...

file generics chapel

share|improve this question

asked Mar 27 at 5:59

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

class Myclass

 var writeflag : bool;
 var output : channel;

 proc init( writeflag = false, filename = "" )
 
 this.writeflag = writeflag;
 if writeflag // (1)
 assert( filename != "" );
 this.output = openwriter( filename );
 // (2)
 


proc main()

 var a = new owned Myclass( writeflag = true,
 filename = "test.out" );
 a.output.writeln( 123 );

share|improve this question

asked Mar 27 at 5:59

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

share|improve this question

asked Mar 27 at 5:59

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

asked Mar 27 at 5:59

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

asked Mar 27 at 5:59

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

2 Answers
2

active

oldest

votes

2

I guess the problem is related to the generic nature of channel (according to the error message), but not very sure how to write such a code appropriately...

You're on the right track. The channel record has some param fields which must be provided at compile-time. You can specify these parameters in the field declaration:

var output : channel(writing=true, kind=iokind.dynamic, locking=false);

share|improve this answer

answered Mar 27 at 13:39

bencraybencray

1,20244 silver badges1616 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks very much, I've confirmed that the code now works. And I have one minor question... Is "locking=false" better than "true" in the above particular case? (Here, I will not write from within a parallel region.) Is locking=false possibly more efficient when only serial write is to be performed?
  
  – roygvib
  Mar 27 at 18:10
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  "locking=false" is indeed more efficient. However, we suggest that you resort to it only in performance-critical code. Also, you'd need to pass "locking=false" to openwriter() as well.
  
  – Vass
  Mar 27 at 22:19
  
  

  
  
  
  

add a comment | 

0

Following the suggestions in the answer and comment, I have modified my code as follows. Because the concrete type is a bit long to remember, I have created a type alias and used it in the class specification (here with locking=true for generality, please see docs).

// utils.chpl
type Writer = channel( true, iokind.dynamic, true );
type Reader = channel( false, iokind.dynamic, true ); 

// test.chpl
use utils only Writer;

class Myclass

 var writeflag : bool;
 var output : Writer;

 // ... the remaining is the same

share|improve this answer

edited Mar 29 at 12:58

answered Mar 29 at 12:08

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

add a comment | 

Your Answer

StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55370697%2fa-field-of-channel-type-gives-error-cannot-default-initialize-a-variable-with%23new-answer', 'question_page');

);

Post as a guest

Name

Email

Required, but never shown

2

I guess the problem is related to the generic nature of channel (according to the error message), but not very sure how to write such a code appropriately...

You're on the right track. The channel record has some param fields which must be provided at compile-time. You can specify these parameters in the field declaration:

var output : channel(writing=true, kind=iokind.dynamic, locking=false);

share|improve this answer

answered Mar 27 at 13:39

bencraybencray

1,20244 silver badges1616 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks very much, I've confirmed that the code now works. And I have one minor question... Is "locking=false" better than "true" in the above particular case? (Here, I will not write from within a parallel region.) Is locking=false possibly more efficient when only serial write is to be performed?
  
  – roygvib
  Mar 27 at 18:10
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  "locking=false" is indeed more efficient. However, we suggest that you resort to it only in performance-critical code. Also, you'd need to pass "locking=false" to openwriter() as well.
  
  – Vass
  Mar 27 at 22:19
  
  

  
  
  
  

add a comment | 

2

I guess the problem is related to the generic nature of channel (according to the error message), but not very sure how to write such a code appropriately...

You're on the right track. The channel record has some param fields which must be provided at compile-time. You can specify these parameters in the field declaration:

var output : channel(writing=true, kind=iokind.dynamic, locking=false);

share|improve this answer

answered Mar 27 at 13:39

bencraybencray

1,20244 silver badges1616 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks very much, I've confirmed that the code now works. And I have one minor question... Is "locking=false" better than "true" in the above particular case? (Here, I will not write from within a parallel region.) Is locking=false possibly more efficient when only serial write is to be performed?
  
  – roygvib
  Mar 27 at 18:10
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  "locking=false" is indeed more efficient. However, we suggest that you resort to it only in performance-critical code. Also, you'd need to pass "locking=false" to openwriter() as well.
  
  – Vass
  Mar 27 at 22:19
  
  

  
  
  
  

add a comment | 

I guess the problem is related to the generic nature of channel (according to the error message), but not very sure how to write such a code appropriately...

You're on the right track. The channel record has some param fields which must be provided at compile-time. You can specify these parameters in the field declaration:

var output : channel(writing=true, kind=iokind.dynamic, locking=false);

share|improve this answer

answered Mar 27 at 13:39

bencraybencray

1,20244 silver badges1616 bronze badges

var output : channel(writing=true, kind=iokind.dynamic, locking=false);

share|improve this answer

answered Mar 27 at 13:39

bencraybencray

1,20244 silver badges1616 bronze badges

answered Mar 27 at 13:39

bencraybencray

1,20244 silver badges1616 bronze badges

answered Mar 27 at 13:39

bencraybencray

1,20244 silver badges1616 bronze badges

0

Following the suggestions in the answer and comment, I have modified my code as follows. Because the concrete type is a bit long to remember, I have created a type alias and used it in the class specification (here with locking=true for generality, please see docs).

// utils.chpl
type Writer = channel( true, iokind.dynamic, true );
type Reader = channel( false, iokind.dynamic, true ); 

// test.chpl
use utils only Writer;

class Myclass

 var writeflag : bool;
 var output : Writer;

 // ... the remaining is the same

share|improve this answer

edited Mar 29 at 12:58

answered Mar 29 at 12:08

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

add a comment | 

0

Following the suggestions in the answer and comment, I have modified my code as follows. Because the concrete type is a bit long to remember, I have created a type alias and used it in the class specification (here with locking=true for generality, please see docs).

// utils.chpl
type Writer = channel( true, iokind.dynamic, true );
type Reader = channel( false, iokind.dynamic, true ); 

// test.chpl
use utils only Writer;

class Myclass

 var writeflag : bool;
 var output : Writer;

 // ... the remaining is the same

share|improve this answer

edited Mar 29 at 12:58

answered Mar 29 at 12:08

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

add a comment | 

Following the suggestions in the answer and comment, I have modified my code as follows. Because the concrete type is a bit long to remember, I have created a type alias and used it in the class specification (here with locking=true for generality, please see docs).

// utils.chpl
type Writer = channel( true, iokind.dynamic, true );
type Reader = channel( false, iokind.dynamic, true ); 

// test.chpl
use utils only Writer;

class Myclass

 var writeflag : bool;
 var output : Writer;

 // ... the remaining is the same

share|improve this answer

edited Mar 29 at 12:58

answered Mar 29 at 12:08

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

// utils.chpl
type Writer = channel( true, iokind.dynamic, true );
type Reader = channel( false, iokind.dynamic, true ); 

// test.chpl
use utils only Writer;

class Myclass

 var writeflag : bool;
 var output : Writer;

 // ... the remaining is the same

share|improve this answer

edited Mar 29 at 12:58

answered Mar 29 at 12:08

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

answered Mar 29 at 12:08

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges

answered Mar 29 at 12:08

roygvibroygvib

5,52522 gold badges1212 silver badges3131 bronze badges