Define an access by key ( structure[key] ) for a custom structure struct?












4












$begingroup$


I have some "complicated" data that I want to encapsulate into a "struct":



For instance (imagine that data have several fields):



data=<|"A"->6,"B"->2|>

var=myType[data]


The advantage is that it is easy to filter your arguments:



doSomething[myType[d_]]:=d



(* usage: *)

doSomething[var]


Now I want to allow this:



var["B"] <- must return 2


But I do not know how to do that, any idea?




What I have done so far:



myType /: Key[k_][myType[d_]:=d[k]


This works for syntax like:



Key["B"][var]


but not for 



var["B"]





associations







share|improve this question











$endgroup$

















    4












    $begingroup$


    I have some "complicated" data that I want to encapsulate into a "struct":



    For instance (imagine that data have several fields):



    data=<|"A"->6,"B"->2|>
    
var=myType[data]


    The advantage is that it is easy to filter your arguments:



    doSomething[myType[d_]]:=d
    

    
(* usage: *)
    
doSomething[var]


    Now I want to allow this:



    var["B"] <- must return 2


    But I do not know how to do that, any idea?




    What I have done so far:



    myType /: Key[k_][myType[d_]:=d[k]


    This works for syntax like:



    Key["B"][var]


    but not for 



    var["B"]





    associations







    share|improve this question











    $endgroup$















      4












      4








      4





      $begingroup$


      I have some "complicated" data that I want to encapsulate into a "struct":



      For instance (imagine that data have several fields):



      data=<|"A"->6,"B"->2|>
      
var=myType[data]


      The advantage is that it is easy to filter your arguments:



      doSomething[myType[d_]]:=d
      

      
(* usage: *)
      
doSomething[var]


      Now I want to allow this:



      var["B"] <- must return 2


      But I do not know how to do that, any idea?




      What I have done so far:



      myType /: Key[k_][myType[d_]:=d[k]


      This works for syntax like:



      Key["B"][var]


      but not for 



      var["B"]





      associations







      share|improve this question











      $endgroup$




      I have some "complicated" data that I want to encapsulate into a "struct":



      For instance (imagine that data have several fields):



      data=<|"A"->6,"B"->2|>
      
var=myType[data]


      The advantage is that it is easy to filter your arguments:



      doSomething[myType[d_]]:=d
      

      
(* usage: *)
      
doSomething[var]


      Now I want to allow this:



      var["B"] <- must return 2


      But I do not know how to do that, any idea?




      What I have done so far:



      myType /: Key[k_][myType[d_]:=d[k]


      This works for syntax like:



      Key["B"][var]


      but not for 



      var["B"]





      associations




      associations






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited yesterday







      Picaud Vincent

















      asked yesterday









      Picaud VincentPicaud Vincent

      1,065517




      1,065517






















          2 Answers
          2






          active

          oldest

          votes


















          4












          $begingroup$

          ClearAll[myType]
          
myType /: myType[data_Association][s_String] := data[[s]]
          

          
var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]



          2







          share|improve this answer









          $endgroup$













          • $begingroup$
            Thanks again Henrik, my questions are too easy :-)
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            You're welcome.
            $endgroup$
            – Henrik Schumacher
            yesterday






          • 2




            $begingroup$
            This definitely works, though it's good to notice that this sets a SubValue for myType, not an UpValue.
            $endgroup$
            – Sjoerd Smit
            yesterday



















          6












          $begingroup$

          You certainly can make the definition you want using TagSetDelayed, but doing so just obfuscates the fact that you aren't setting an UpValue at all, as was pointed out in the comment above.



          The direct way to set this definition is just



          myType[assoc_?AssociationQ][key_] := assoc[key]


          Doing it like this makes it clear what you are doing. Looking at the code with TagSetDelayed you has to stare at it for a second wondering what the actual definition is, whereas this definition is clear.



          On a side note, if you want a more restrictive definition, one that only applies when the key is present in the association you could use



          myType[KeyValuePattern[{key_ -> val_}]][key_] := val


          which returns unevaluated when the key isn't present



          var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]
          
(* 2 *)
          

          
var["E"]
          
(* myType[<|"A" -> 6, "B" -> 2|>]["E"] *)





          share|improve this answer









          $endgroup$













          • $begingroup$
            thanks for the clarifications
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            to be nit-picking using TagSetDelayed does not really mean trying to set an UpValue, it just more explicitly states to which symbol the rule should be associated. Of course in practice the only relevant case where you would use it is for setting UpValues as for every other possibility (DownValues and SubValues) the default is all that is possible to choose and using TagSetDelayed in those cases is redundant...
            $endgroup$
            – Albert Retey
            13 hours ago











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          2 Answers
          2






          active

          oldest

          votes








          2 Answers
          2






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          4












          $begingroup$

          ClearAll[myType]
          
myType /: myType[data_Association][s_String] := data[[s]]
          

          
var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]



          2







          share|improve this answer









          $endgroup$













          • $begingroup$
            Thanks again Henrik, my questions are too easy :-)
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            You're welcome.
            $endgroup$
            – Henrik Schumacher
            yesterday






          • 2




            $begingroup$
            This definitely works, though it's good to notice that this sets a SubValue for myType, not an UpValue.
            $endgroup$
            – Sjoerd Smit
            yesterday
















          4












          $begingroup$

          ClearAll[myType]
          
myType /: myType[data_Association][s_String] := data[[s]]
          

          
var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]



          2







          share|improve this answer









          $endgroup$













          • $begingroup$
            Thanks again Henrik, my questions are too easy :-)
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            You're welcome.
            $endgroup$
            – Henrik Schumacher
            yesterday






          • 2




            $begingroup$
            This definitely works, though it's good to notice that this sets a SubValue for myType, not an UpValue.
            $endgroup$
            – Sjoerd Smit
            yesterday














          4












          4








          4





          $begingroup$

          ClearAll[myType]
          
myType /: myType[data_Association][s_String] := data[[s]]
          

          
var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]



          2







          share|improve this answer









          $endgroup$



          ClearAll[myType]
          
myType /: myType[data_Association][s_String] := data[[s]]
          

          
var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]



          2








          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered yesterday









          Henrik SchumacherHenrik Schumacher

          52.1k470147




          52.1k470147












          • $begingroup$
            Thanks again Henrik, my questions are too easy :-)
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            You're welcome.
            $endgroup$
            – Henrik Schumacher
            yesterday






          • 2




            $begingroup$
            This definitely works, though it's good to notice that this sets a SubValue for myType, not an UpValue.
            $endgroup$
            – Sjoerd Smit
            yesterday


















          • $begingroup$
            Thanks again Henrik, my questions are too easy :-)
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            You're welcome.
            $endgroup$
            – Henrik Schumacher
            yesterday






          • 2




            $begingroup$
            This definitely works, though it's good to notice that this sets a SubValue for myType, not an UpValue.
            $endgroup$
            – Sjoerd Smit
            yesterday
















          $begingroup$
          Thanks again Henrik, my questions are too easy :-)
          $endgroup$
          – Picaud Vincent
          yesterday




          $begingroup$
          Thanks again Henrik, my questions are too easy :-)
          $endgroup$
          – Picaud Vincent
          yesterday












          $begingroup$
          You're welcome.
          $endgroup$
          – Henrik Schumacher
          yesterday




          $begingroup$
          You're welcome.
          $endgroup$
          – Henrik Schumacher
          yesterday




          2




          2




          $begingroup$
          This definitely works, though it's good to notice that this sets a SubValue for myType, not an UpValue.
          $endgroup$
          – Sjoerd Smit
          yesterday




          $begingroup$
          This definitely works, though it's good to notice that this sets a SubValue for myType, not an UpValue.
          $endgroup$
          – Sjoerd Smit
          yesterday











          6












          $begingroup$

          You certainly can make the definition you want using TagSetDelayed, but doing so just obfuscates the fact that you aren't setting an UpValue at all, as was pointed out in the comment above.



          The direct way to set this definition is just



          myType[assoc_?AssociationQ][key_] := assoc[key]


          Doing it like this makes it clear what you are doing. Looking at the code with TagSetDelayed you has to stare at it for a second wondering what the actual definition is, whereas this definition is clear.



          On a side note, if you want a more restrictive definition, one that only applies when the key is present in the association you could use



          myType[KeyValuePattern[{key_ -> val_}]][key_] := val


          which returns unevaluated when the key isn't present



          var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]
          
(* 2 *)
          

          
var["E"]
          
(* myType[<|"A" -> 6, "B" -> 2|>]["E"] *)





          share|improve this answer









          $endgroup$













          • $begingroup$
            thanks for the clarifications
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            to be nit-picking using TagSetDelayed does not really mean trying to set an UpValue, it just more explicitly states to which symbol the rule should be associated. Of course in practice the only relevant case where you would use it is for setting UpValues as for every other possibility (DownValues and SubValues) the default is all that is possible to choose and using TagSetDelayed in those cases is redundant...
            $endgroup$
            – Albert Retey
            13 hours ago
















          6












          $begingroup$

          You certainly can make the definition you want using TagSetDelayed, but doing so just obfuscates the fact that you aren't setting an UpValue at all, as was pointed out in the comment above.



          The direct way to set this definition is just



          myType[assoc_?AssociationQ][key_] := assoc[key]


          Doing it like this makes it clear what you are doing. Looking at the code with TagSetDelayed you has to stare at it for a second wondering what the actual definition is, whereas this definition is clear.



          On a side note, if you want a more restrictive definition, one that only applies when the key is present in the association you could use



          myType[KeyValuePattern[{key_ -> val_}]][key_] := val


          which returns unevaluated when the key isn't present



          var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]
          
(* 2 *)
          

          
var["E"]
          
(* myType[<|"A" -> 6, "B" -> 2|>]["E"] *)





          share|improve this answer









          $endgroup$













          • $begingroup$
            thanks for the clarifications
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            to be nit-picking using TagSetDelayed does not really mean trying to set an UpValue, it just more explicitly states to which symbol the rule should be associated. Of course in practice the only relevant case where you would use it is for setting UpValues as for every other possibility (DownValues and SubValues) the default is all that is possible to choose and using TagSetDelayed in those cases is redundant...
            $endgroup$
            – Albert Retey
            13 hours ago














          6












          6








          6





          $begingroup$

          You certainly can make the definition you want using TagSetDelayed, but doing so just obfuscates the fact that you aren't setting an UpValue at all, as was pointed out in the comment above.



          The direct way to set this definition is just



          myType[assoc_?AssociationQ][key_] := assoc[key]


          Doing it like this makes it clear what you are doing. Looking at the code with TagSetDelayed you has to stare at it for a second wondering what the actual definition is, whereas this definition is clear.



          On a side note, if you want a more restrictive definition, one that only applies when the key is present in the association you could use



          myType[KeyValuePattern[{key_ -> val_}]][key_] := val


          which returns unevaluated when the key isn't present



          var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]
          
(* 2 *)
          

          
var["E"]
          
(* myType[<|"A" -> 6, "B" -> 2|>]["E"] *)





          share|improve this answer









          $endgroup$



          You certainly can make the definition you want using TagSetDelayed, but doing so just obfuscates the fact that you aren't setting an UpValue at all, as was pointed out in the comment above.



          The direct way to set this definition is just



          myType[assoc_?AssociationQ][key_] := assoc[key]


          Doing it like this makes it clear what you are doing. Looking at the code with TagSetDelayed you has to stare at it for a second wondering what the actual definition is, whereas this definition is clear.



          On a side note, if you want a more restrictive definition, one that only applies when the key is present in the association you could use



          myType[KeyValuePattern[{key_ -> val_}]][key_] := val


          which returns unevaluated when the key isn't present



          var = myType[<|"A" -> 6, "B" -> 2|>];
          
var["B"]
          
(* 2 *)
          

          
var["E"]
          
(* myType[<|"A" -> 6, "B" -> 2|>]["E"] *)






          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered yesterday









          Jason B.Jason B.

          48.3k388190




          48.3k388190












          • $begingroup$
            thanks for the clarifications
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            to be nit-picking using TagSetDelayed does not really mean trying to set an UpValue, it just more explicitly states to which symbol the rule should be associated. Of course in practice the only relevant case where you would use it is for setting UpValues as for every other possibility (DownValues and SubValues) the default is all that is possible to choose and using TagSetDelayed in those cases is redundant...
            $endgroup$
            – Albert Retey
            13 hours ago


















          • $begingroup$
            thanks for the clarifications
            $endgroup$
            – Picaud Vincent
            yesterday










          • $begingroup$
            to be nit-picking using TagSetDelayed does not really mean trying to set an UpValue, it just more explicitly states to which symbol the rule should be associated. Of course in practice the only relevant case where you would use it is for setting UpValues as for every other possibility (DownValues and SubValues) the default is all that is possible to choose and using TagSetDelayed in those cases is redundant...
            $endgroup$
            – Albert Retey
            13 hours ago
















          $begingroup$
          thanks for the clarifications
          $endgroup$
          – Picaud Vincent
          yesterday




          $begingroup$
          thanks for the clarifications
          $endgroup$
          – Picaud Vincent
          yesterday












          $begingroup$
          to be nit-picking using TagSetDelayed does not really mean trying to set an UpValue, it just more explicitly states to which symbol the rule should be associated. Of course in practice the only relevant case where you would use it is for setting UpValues as for every other possibility (DownValues and SubValues) the default is all that is possible to choose and using TagSetDelayed in those cases is redundant...
          $endgroup$
          – Albert Retey
          13 hours ago




          $begingroup$
          to be nit-picking using TagSetDelayed does not really mean trying to set an UpValue, it just more explicitly states to which symbol the rule should be associated. Of course in practice the only relevant case where you would use it is for setting UpValues as for every other possibility (DownValues and SubValues) the default is all that is possible to choose and using TagSetDelayed in those cases is redundant...
          $endgroup$
          – Albert Retey
          13 hours ago


















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