Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
Am 23.12.2022 um 15:50 schrieb Andrew Haines via fpc-pascal:
Error: Ordinal expression expected
[TEnumAttr(['YES', 'NO', 'COULD_BE'])]
There is another (and cleaner) approach that uses an abstract attribute
class. See attachment.
The advantage is that the compiler warns you with an error when you add
a new value to the enum and you don't declare a string value for it.
Ondrej
program EnumAttrTest;
{$mode objfpc}{$H+}
{$modeswitch prefixedattributes}
uses
SysUtils, TypInfo;
type
EnumValues = class(TCustomAttribute)
public
function OrdToStr(const aValue: Integer): string; virtual; abstract;
constructor Create;
end;
MyEnumValues = class(EnumValues)
public
function OrdToStr(const aValue: Integer): string; override;
end;
[MyEnumValues]
TMyEnum = (meYes, meNo, meCouldBe);
{ EnumValues }
constructor EnumValues.Create;
begin
end;
{ MyEnumValues }
function MyEnumValues.OrdToStr(const aValue: Integer): string;
const
cValues: array[TMyEnum] of string = ('YES', 'NO', 'COULD_BE');
begin
Result := cValues[TMyEnum(aValue)];
end;
procedure WriteAllValues(const aTypInfo: PTypeInfo);
var
xAttrs: PAttributeTable;
xAttr: TCustomAttribute;
I, V: Integer;
begin
xAttrs := GetAttributeTable(aTypInfo);
for I := 0 to xAttrs^.AttributeCount-1 do
begin
xAttr := GetAttribute(xAttrs, I);
try
if xAttr is EnumValues then
begin
for V := 0 to GetTypeData(aTypInfo)^.MaxValue do
Writeln(EnumValues(xAttr).OrdToStr(V));
end;
finally
xAttr.Free;
end;
end;
end;
begin
WriteAllValues(PTypeInfo(TypeInfo(TMyEnum)));
ReadLn;
end.
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Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
On 23.12.2022 15:50, Andrew Haines via fpc-pascal wrote: On 12/23/22 5:24 AM, Ondrej Pokorny via fpc-pascal wrote: This may be simpler: [TEnumAttr(['YES', 'NO', 'COULD_BE'])] TMyEnum = (meYes, meNo, meCouldBe); TEnumAttr = class(TCustomAttribute) protected FValues: TStringArray; FTypeName: String; public class function FromType(ATypeInfo: PTypeInfo): TEnumAttr; constructor Create(Values: array of string); I tried that first but the compiler gave an error on the "[" Error: Ordinal expression expected [TEnumAttr(['YES', 'NO', 'COULD_BE'])] Indeed. I would say that is a bug and therefore I reported it: https://gitlab.com/freepascal.org/fpc/source/-/issues/40058 I usually use the scoped enums but in case the enum values are not valid identifiers this is the perfect way to handle them. Therefore thanks for the idea :) I use attributes for various things but didn't realize this possibility. Ondrej ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
On Fri, 23 Dec 2022, Sven Barth wrote: Michael Van Canneyt via fpc-pascal schrieb am Fr., 23. Dez. 2022, 10:48: On Fri, 23 Dec 2022, Sven Barth via fpc-pascal wrote: Michael Van Canneyt via fpc-pascal schrieb am Fr., 23. Dez. 2022, 08:18: On Thu, 22 Dec 2022, Andrew Haines via fpc-pascal wrote: Hi what I want to do is similar to this question here: https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/ I am going to create multiple type helpers for enums and I would like to look up the helper and use common methods AsString AsOrdinal to get/set the values. I am recieving them as json that I dont have control over. I am using typeinfo to fill in all the properties but I would like to convert the strings I am receiving to the enum values semi-automatically. LString := 'STATUS'; LHelper := GetHelper(LPropInfo^.PropType); // enum proptype Since there can be multiple type helpers for a type, this will never be possible. At best you would get a list. But I don't think there is even a list of type helpers per type. Sven will need to confirm. As the active helper(s) for a type change(s) depending on the current scope (e.g. in unit A it might be a different helper than in unit B) this is not possible. Also helpers are not in any way usable on their own except to retrieve their RTTI information. But theoretically it should be possible to generate and get a list of all defined type helpers, whether they are in scope or not ? No, because the compiler doesn't keep track of that. It's only interested in what is in scope *right now*. I understand such a list is not kept now. That's why I said "theoretically" as in "it is possible to add to the compiler" To be clear: I don't think you should add such a list, I'm simply interested in the possibility of such a thing. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
On 12/23/22 5:24 AM, Ondrej Pokorny via fpc-pascal wrote:
This may be simpler:
[TEnumAttr(['YES', 'NO', 'COULD_BE'])]
TMyEnum = (meYes, meNo, meCouldBe);
TEnumAttr = class(TCustomAttribute)
protected
FValues: TStringArray;
FTypeName: String;
public
class function FromType(ATypeInfo: PTypeInfo): TEnumAttr;
constructor Create(Values: array of string);
---
I tried that first but the compiler gave an error on the "["
Error: Ordinal expression expected
[TEnumAttr(['YES', 'NO', 'COULD_BE'])]
Or, if the enum values are valid identifiers, you can simple use
scoped enums:
{$SCOPEDENUMS ON}
TMyEnum = (YES, NO, COULD_BE);
and the usual TypeInfo methods.
Ondrej
I didn't know about those, that could also be a good solution, thanks!
Andrew
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Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
Michael Van Canneyt via fpc-pascal schrieb am Fr., 23. Dez. 2022, 10:48: > > > On Fri, 23 Dec 2022, Sven Barth via fpc-pascal wrote: > > > Michael Van Canneyt via fpc-pascal > > schrieb am Fr., 23. Dez. 2022, 08:18: > > > >> > >> > >> On Thu, 22 Dec 2022, Andrew Haines via fpc-pascal wrote: > >> > >>> Hi what I want to do is similar to this question here: > >>> > >> > https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/ > >>> > >>> I am going to create multiple type helpers for enums and I would like > to > >> look > >>> up the helper and use common methods AsString AsOrdinal to get/set the > >>> values. I am recieving them as json that I dont have control over. I am > >> using > >>> typeinfo to fill in all the properties but I would like to convert the > >>> strings I am receiving to the enum values semi-automatically. > >>> > >>> LString := 'STATUS'; > >>> > >>> LHelper := GetHelper(LPropInfo^.PropType); // enum proptype > >> > >> Since there can be multiple type helpers for a type, this will never be > >> possible. At best you would get a list. > >> > >> But I don't think there is even a list of type helpers per type. > >> Sven will need to confirm. > >> > > > > As the active helper(s) for a type change(s) depending on the current > scope > > (e.g. in unit A it might be a different helper than in unit B) this is > not > > possible. Also helpers are not in any way usable on their own except to > > retrieve their RTTI information. > > But theoretically it should be possible to generate and get a list of all > defined type helpers, whether they are in scope or not ? > No, because the compiler doesn't keep track of that. It's only interested in what is in scope *right now*. > If their RTTI could include a function that returns an interface, you could > retrieve that and do as the OP suggests.. > Don't make helpers to something that they're simply not there for. Regards, Sven ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
This may be simpler:
[TEnumAttr(['YES', 'NO', 'COULD_BE'])]
TMyEnum = (meYes, meNo, meCouldBe);
TEnumAttr = class(TCustomAttribute)
protected
FValues: TStringArray;
FTypeName: String;
public
class function FromType(ATypeInfo: PTypeInfo): TEnumAttr;
constructor Create(Values: array of string);
---
Or, if the enum values are valid identifiers, you can simple use scoped
enums:
{$SCOPEDENUMS ON}
TMyEnum = (YES, NO, COULD_BE);
and the usual TypeInfo methods.
Ondrej
On 23.12.2022 06:35, Andrew Haines via fpc-pascal wrote:
So, I came up with a solution using Custom Attributes.
I can declare this:
[TEnumAttr('YES', 'NO', 'COULD_BE')]
TMyEnum = (meYes, meNo, meCouldBe);
and at runtime look for the TEnumAttr attribute and use that.
TEnumAttr = class(TCustomAttribute)
protected
FValues: TStringArray;
FTypeName: String;
public
class function FromType(ATypeInfo: PTypeInfo): TEnumAttr;
constructor Create(Val1: String);
constructor Create(Val1, Val2: String);
etc
Maybe this can help someone else with a similar use case.
Regards,
Andrew Haines
On 12/22/22 8:40 PM, Andrew Haines via fpc-pascal wrote:
Hi what I want to do is similar to this question here:
https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/
I am going to create multiple type helpers for enums and I would like
to look up the helper and use common methods AsString AsOrdinal to
get/set the values. I am recieving them as json that I dont have
control over. I am using typeinfo to fill in all the properties but I
would like to convert the strings I am receiving to the enum values
semi-automatically.
LString := 'STATUS';
LHelper := GetHelper(LPropInfo^.PropType); // enum proptype
LToStringInterface := LHelper as IToStringInterface;
SetOrdProp(LObject, 'propname', LToStringInterface.OrdValue(LString);
Something like that. I'm not sure if it's even possible to find the
helper type with typeinfo.
Thanks for your suggestions :)
Regards,
Andrew
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Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
On Fri, 23 Dec 2022, Sven Barth via fpc-pascal wrote: Michael Van Canneyt via fpc-pascal schrieb am Fr., 23. Dez. 2022, 08:18: On Thu, 22 Dec 2022, Andrew Haines via fpc-pascal wrote: Hi what I want to do is similar to this question here: https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/ I am going to create multiple type helpers for enums and I would like to look up the helper and use common methods AsString AsOrdinal to get/set the values. I am recieving them as json that I dont have control over. I am using typeinfo to fill in all the properties but I would like to convert the strings I am receiving to the enum values semi-automatically. LString := 'STATUS'; LHelper := GetHelper(LPropInfo^.PropType); // enum proptype Since there can be multiple type helpers for a type, this will never be possible. At best you would get a list. But I don't think there is even a list of type helpers per type. Sven will need to confirm. As the active helper(s) for a type change(s) depending on the current scope (e.g. in unit A it might be a different helper than in unit B) this is not possible. Also helpers are not in any way usable on their own except to retrieve their RTTI information. But theoretically it should be possible to generate and get a list of all defined type helpers, whether they are in scope or not ? If their RTTI could include a function that returns an interface, you could retrieve that and do as the OP suggests... I think the OP's solution with attributes is the same as the one TMS Software's Aurelius ORM uses. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
Michael Van Canneyt via fpc-pascal schrieb am Fr., 23. Dez. 2022, 08:18: > > > On Thu, 22 Dec 2022, Andrew Haines via fpc-pascal wrote: > > > Hi what I want to do is similar to this question here: > > > https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/ > > > > I am going to create multiple type helpers for enums and I would like to > look > > up the helper and use common methods AsString AsOrdinal to get/set the > > values. I am recieving them as json that I dont have control over. I am > using > > typeinfo to fill in all the properties but I would like to convert the > > strings I am receiving to the enum values semi-automatically. > > > > LString := 'STATUS'; > > > > LHelper := GetHelper(LPropInfo^.PropType); // enum proptype > > Since there can be multiple type helpers for a type, this will never be > possible. At best you would get a list. > > But I don't think there is even a list of type helpers per type. > Sven will need to confirm. > As the active helper(s) for a type change(s) depending on the current scope (e.g. in unit A it might be a different helper than in unit B) this is not possible. Also helpers are not in any way usable on their own except to retrieve their RTTI information. Regards, Sven ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
On Thu, 22 Dec 2022, Andrew Haines via fpc-pascal wrote: Hi what I want to do is similar to this question here: https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/ I am going to create multiple type helpers for enums and I would like to look up the helper and use common methods AsString AsOrdinal to get/set the values. I am recieving them as json that I dont have control over. I am using typeinfo to fill in all the properties but I would like to convert the strings I am receiving to the enum values semi-automatically. LString := 'STATUS'; LHelper := GetHelper(LPropInfo^.PropType); // enum proptype Since there can be multiple type helpers for a type, this will never be possible. At best you would get a list. But I don't think there is even a list of type helpers per type. Sven will need to confirm. In your case, I would simply register a function that does this for each known enum type. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
So, I came up with a solution using Custom Attributes.
I can declare this:
[TEnumAttr('YES', 'NO', 'COULD_BE')]
TMyEnum = (meYes, meNo, meCouldBe);
and at runtime look for the TEnumAttr attribute and use that.
TEnumAttr = class(TCustomAttribute)
protected
FValues: TStringArray;
FTypeName: String;
public
class function FromType(ATypeInfo: PTypeInfo): TEnumAttr;
constructor Create(Val1: String);
constructor Create(Val1, Val2: String);
etc
Maybe this can help someone else with a similar use case.
Regards,
Andrew Haines
On 12/22/22 8:40 PM, Andrew Haines via fpc-pascal wrote:
Hi what I want to do is similar to this question here:
https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/
I am going to create multiple type helpers for enums and I would like
to look up the helper and use common methods AsString AsOrdinal to
get/set the values. I am recieving them as json that I dont have
control over. I am using typeinfo to fill in all the properties but I
would like to convert the strings I am receiving to the enum values
semi-automatically.
LString := 'STATUS';
LHelper := GetHelper(LPropInfo^.PropType); // enum proptype
LToStringInterface := LHelper as IToStringInterface;
SetOrdProp(LObject, 'propname', LToStringInterface.OrdValue(LString);
Something like that. I'm not sure if it's even possible to find the
helper type with typeinfo.
Thanks for your suggestions :)
Regards,
Andrew
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[fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?
Hi what I want to do is similar to this question here: https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/ I am going to create multiple type helpers for enums and I would like to look up the helper and use common methods AsString AsOrdinal to get/set the values. I am recieving them as json that I dont have control over. I am using typeinfo to fill in all the properties but I would like to convert the strings I am receiving to the enum values semi-automatically. LString := 'STATUS'; LHelper := GetHelper(LPropInfo^.PropType); // enum proptype LToStringInterface := LHelper as IToStringInterface; SetOrdProp(LObject, 'propname', LToStringInterface.OrdValue(LString); Something like that. I'm not sure if it's even possible to find the helper type with typeinfo. Thanks for your suggestions :) Regards, Andrew ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
