record: C# like records for D
[DUB](https://code.dlang.org/packages/record)
[Github](https://github.com/hmmdyl/record)
This is record. It aims to implement records similar to what C#
has by leveraging D's metaprogramming. [C# Example
1](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/records) [C# Example 2](https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/records).
Future steps are going to be adding a record struct; default
value support; init-only-setters like in C#, wherein at the end
of construction or duplication, the init lambda for the field is
called, and the field can be set that once.
Example:
```D
import drecord;
alias MyRecord = record!(
get!(int, "x"), /// x is an int, can only be set during
construction
get_set!(float, "y"), /// y is a float, can be get or set
whenever
property!("getDoubleOfX", (r) => r.x * 2), /// a property
that returns the double of x
property!("getMultipleOfX", (r, m) => r.x * m, int), /// that
takes an argument and multiples x by that value
property!("printY", (r) => writeln(r.y)), /// prints y
property!("resetY", (r) => r.y = 0) /// resets y to 0f
);
auto r = new MyRecord(12, 4.5f); /// sets x, y
writeln(r); // { x = 12, y = 4.5f }
writeln(r.toHash); // 376
writeln(r.x); // 12
writeln(r.getDoubleOfX); // 24
writeln(r.getMultipleOfX(4)); // 48
r.printY; // 4.5
r.resetY;
writeln(r.y); // 0
r.y = 13f;
r.printY; // 13
/// Duplicate r, and set x to 17 (we can only do this in ctor, or
during duplication)
/// This is equivalent to C#'s "with" syntax for records
auto q = r.duplicate!("x")(17);
writeln(q); // {x = 17, y = 0}
writeln(q == r); // false
writeln(q is r); // false
auto b = r.duplicate; // duplicate, don't change any fields
writeln(b == r); // true
writeln(b is r); // false
```
Re: record: C# like records for D
On Wednesday, 14 July 2021 at 23:16:05 UTC, Dylan Graham wrote:
[DUB](https://code.dlang.org/packages/record)
[Github](https://github.com/hmmdyl/record)
record now has support for custom default initialisers. Example:
```D
import drecord;
alias DefaultRecord = record!(
// The third parameter is a lambda which provides default
initialisation
get!(int, "x", () => 4), // x is set to 4 by default
get_set(Object, "o", () => new Object) // o is set to a new
Object by default
);
auto r = new DefaultRecord; // run the default initialisers
writeln(r); // {x = 4, o = object.Object}
auto q = DefaultRecord.create!"x"(9); // run default
initialisers, then set x to 9
writeln(r); // {x = 9, o = object.Object}
```
Re: record: C# like records for D
On Wednesday, 14 July 2021 at 23:16:05 UTC, Dylan Graham wrote:
... init-only-setters like in C#, wherein at the end of
construction or duplication, the init lambda for the field is
called, and the field can be set that once.
This has been implemented with `get_compute`. Example:
```D
alias MyRecord = record!(
get!(int, "x", () => 20),
// get_compute lets you compute a field after the rest have
been initialised
get_compute!(float, "y", (rec) => rec.x * 2f)
);
auto r = new MyRecord;
writeln(r); // {x = 20, y = 40f}
r = new MyRecord(10);
writeln(r); // {x = 10, y = 20f}
r = MyRecord.create!"x"(5);
writeln(r); // {x = 5, y = 10f}
auto q = r.duplicate!"x"(2);
writeln(q); // {x = 2, y = 4f}
```
Re: record: C# like records for D
On Wednesday, 14 July 2021 at 23:16:05 UTC, Dylan Graham wrote:
[DUB](https://code.dlang.org/packages/record)
[Github](https://github.com/hmmdyl/record)
Found and squashed some critical bugs. Thanks to Adam and Rikki
for the help.
Before, record would throw a compilation error due when passed
types declared outside of drecord or its imports. Example:
```D
module myapp;
class A{}
auto MyRecord = record!(get!(A, "a")); // would throw an error as
it could not find A
```
This was due to improper usage of `.stringof` and mixins. This
has been corrected and replaced with idiomatic D. The string
generation functions for the constructor and opEquals have been
removed and replaced in accordance to above.
Re: record: C# like records for D
On Friday, 16 July 2021 at 13:14:22 UTC, Dylan Graham wrote:
On Wednesday, 14 July 2021 at 23:16:05 UTC, Dylan Graham wrote:
[DUB](https://code.dlang.org/packages/record)
[Github](https://github.com/hmmdyl/record)
```D
module myapp;
class A{}
auto MyRecord = record!(get!(A, "a")); // would throw an error
as it could not find A
```
That should read
```D
[...]
alias MyRecord = record!(get!(A, "a")); // would throw an error
```
Re: record: C# like records for D
On Wednesday, 14 July 2021 at 23:16:05 UTC, Dylan Graham wrote: [DUB](https://code.dlang.org/packages/record) [Github](https://github.com/hmmdyl/record) This is record. It aims to implement records similar to what C# has by leveraging D's metaprogramming. [C# Example 1](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/records) [C# Example 2](https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/records). Future steps are going to be adding a record struct; default value support; init-only-setters like in C#, wherein at the end of construction or duplication, the init lambda for the field is called, and the field can be set that once. What adventage has record over normal immutable/const class?
Re: record: C# like records for D
On Friday, 16 July 2021 at 13:54:36 UTC, vit wrote: On Wednesday, 14 July 2021 at 23:16:05 UTC, Dylan Graham wrote: [DUB](https://code.dlang.org/packages/record) [Github](https://github.com/hmmdyl/record) This is record. It aims to implement records similar to what C# has by leveraging D's metaprogramming. [C# Example 1](https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/types/records) [C# Example 2](https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/records). Future steps are going to be adding a record struct; default value support; init-only-setters like in C#, wherein at the end of construction or duplication, the init lambda for the field is called, and the field can be set that once. What adventage has record over normal immutable/const class? In terms of mutability, none. The duplicate method, however, lets you copy and mutate (once at duplication) a record without impacting the integrity of the original. You can do this with an immutable class, but then you have to roll your own. Really, it's more a convenience / less typing sort of feature, as it implements all the common boilerplate for you, which should help with consistency of code.
Re: record: C# like records for D
On 7/16/21 10:52 AM, Dylan Graham wrote:
On Friday, 16 July 2021 at 13:54:36 UTC, vit wrote:
What adventage has record over normal immutable/const class?
In terms of mutability, none.
The duplicate method, however, lets you copy and mutate (once at
duplication) a record without impacting the integrity of the original.
You can do this with an immutable class, but then you have to roll your
own.
Really, it's more a convenience / less typing sort of feature, as it
implements all the common boilerplate for you, which should help with
consistency of code.
What about a UFCS `duplicate` method?
I'm not doubting there are good reasons to define types this way in C#,
but D has pretty good tools when it comes to boilerplate.
I would possibly suggest that instead of a record template that accepts
directives using inline lambdas, etc, just accept a model type and use
udas to adjust the record type.
i.e.:
```d
struct RecModel {
@get_set float y;
@get int x;
auto getDoubleOfX() { return x * 2; }
... // etc
}
alias MyRecord = record!RecModel;
```
I use this kind of thing to great success in my SQL database system.
-Steve
Re: record: C# like records for D
On Friday, 16 July 2021 at 19:37:53 UTC, Steven Schveighoffer
wrote:
On 7/16/21 10:52 AM, Dylan Graham wrote:
On Friday, 16 July 2021 at 13:54:36 UTC, vit wrote:
What adventage has record over normal immutable/const class?
In terms of mutability, none.
The duplicate method, however, lets you copy and mutate (once
at duplication) a record without impacting the integrity of
the original. You can do this with an immutable class, but
then you have to roll your own.
Really, it's more a convenience / less typing sort of feature,
as it implements all the common boilerplate for you, which
should help with consistency of code.
What about a UFCS `duplicate` method?
I'm not doubting there are good reasons to define types this
way in C#, but D has pretty good tools when it comes to
boilerplate.
I would possibly suggest that instead of a record template that
accepts directives using inline lambdas, etc, just accept a
model type and use udas to adjust the record type.
i.e.:
```d
struct RecModel {
@get_set float y;
@get int x;
auto getDoubleOfX() { return x * 2; }
... // etc
}
alias MyRecord = record!RecModel;
```
I use this kind of thing to great success in my SQL database
system.
-Steve
That is a good idea, and to be honest I haven't looked at it that
way. So the record is a separate type from its model? Ie: `class
MyRecord {}` based off `struct RecordModel {}`? Or did I
misunderstand?
With regards to things like properties and methods, do you have
RecModel inlined in the class and then forward the calls to it?
Ie:
```D
struct RecModel {
@get int x;
auto doubleOfX() { return x; }
}
class Rec {
private RecModel instance;
@property auto x() { return instance.x; }
auto doubleOfX() { return instance.doubleOfX; }
}
```
I do like the lambda directives as it, in my mind at least,
enforces the idea that the record/class must be a simple data
type (ie no crazy methods and such).
I do have to admit this was more an exercise in metaprogramming,
and since I did manage to make something I figured I'd share it.
Re: record: C# like records for D
On 7/16/21 4:11 PM, Dylan Graham wrote:
On Friday, 16 July 2021 at 19:37:53 UTC, Steven Schveighoffer wrote:
I would possibly suggest that instead of a record template that
accepts directives using inline lambdas, etc, just accept a model type
and use udas to adjust the record type.
That is a good idea, and to be honest I haven't looked at it that way.
So the record is a separate type from its model? Ie: `class MyRecord {}`
based off `struct RecordModel {}`? Or did I misunderstand?
With regards to things like properties and methods, do you have RecModel
inlined in the class and then forward the calls to it? Ie:
```D
struct RecModel {
@get int x;
auto doubleOfX() { return x; }
}
class Rec {
private RecModel instance;
@property auto x() { return instance.x; }
auto doubleOfX() { return instance.doubleOfX; }
}
```
Yeah, something like that. Though there are multiple ways to go about
it. One is to write a string that represents what you want it to do, and
then mixin that thing. The way I do it is using `opDispatch` which is
super-powerful for forwarding calls like that. I'm assuming you are
already doing something like this anyway! It's just, what are the
instructions?
I really can't wait to reveal the sql library I've been nursing along
with my web project. I don't want to post it yet here, because it will
just garner more questions.
I can point you at some early ideas I had on this kind of model-based
programming, in a Boston meetup I did a talk for a number of years ago:
https://www.youtube.com/watch?v=ZxzczSDaobw
I do like the lambda directives as it, in my mind at least, enforces the
idea that the record/class must be a simple data type (ie no crazy
methods and such).
I'm not sure what you think is a "crazy" method, but lambdas can do
whatever a method can do.
I like using models vs. template directives because you get to use the
actual language to enforce your "model" is sane, and to make readable
instructions for the metaprogramming processor. Like in one of your
methods, you have:
```d
property!("getMultipleOfX", (r, m) => r.x * m, int)
```
What is that `int` for? It's not clear from the usage, I have to go look
it up. Most likely, it's the return type, but it's not nearly as clear as:
```d
int getMultipleOfX(int m) { return x * m; }
```
Plus, I can debug my model without having to debug the metaprogramming
stuff.
I do have to admit this was more an exercise in metaprogramming, and
since I did manage to make something I figured I'd share it.
It's cool, I love using metaprogramming to write code for me. It's
without a doubt the best reason to use D. Learning how to use to avoid
writing boilerplate is life changing!
-Steve
