Re: Error: function `...` without `this` cannot be `const`
On Wednesday, 30 June 2021 at 20:12:29 UTC, H. S. Teoh wrote:
On Wed, Jun 30, 2021 at 07:40:40PM +, someone via
Digitalmars-d-learn wrote: [...]
@property int data() { return m_data; } // read property
[...]
string something() @property { return this.whatever; }
[...]
Now I am not sure which is the correct way.
[...]
Both are correct. :-) It's up to personal style preference.
T
Just to remark here, if you want to apply const to a return type
put it inside brackets like: const(MyClass) foo(); otherwise
compiler will try to apply it to 'this' parameter.
Best regards,
Alexandru.
Re: Error: function `...` without `this` cannot be `const`
On Wednesday, 30 June 2021 at 20:12:29 UTC, H. S. Teoh wrote:
On Wed, Jun 30, 2021 at 07:40:40PM +, someone via
Digitalmars-d-learn wrote: [...]
@property int data() { return m_data; } // read property
[...]
string something() @property { return this.whatever; }
[...]
Now I am not sure which is the correct way.
[...]
Both are correct. :-) It's up to personal style preference.
T
@nogc unittest { } // works
unittest @nogc { } // doesn't work
https://dlang.org/dstyle.html doesn't suggest either way, but
does suggest alphabetical ordering(!) which I hadn't noticed.
Re: Error: function `...` without `this` cannot be `const`
On Wed, Jun 30, 2021 at 07:40:40PM +, someone via Digitalmars-d-learn wrote:
[...]
> @property int data() { return m_data; } // read property
[...]
> string something() @property { return this.whatever; }
[...]
> Now I am not sure which is the correct way.
[...]
Both are correct. :-) It's up to personal style preference.
T
--
2+2=4. 2*2=4. 2^2=4. Therefore, +, *, and ^ are the same operation.
Re: Error: function `...` without `this` cannot be `const`
On Wednesday, 30 June 2021 at 18:10:52 UTC, Alexandru Ermicioi
wrote:
That is because const/immutable/shared are being applied on the
object hence 'this' variable inside function body if function
is a member of a struct or class.
So this will make sense ONLY for an object's method right ?
It doesn't make sense to have a const modifier on a simple
function. What will that const mean then in context of that
function? To what it will be applied?
I think of all the code I have I choose the worst example for
asking advice on attribute placement !
Let's use @property instead of const:
```d
struct Foo
{
@property int data() { return m_data; } // read property
@property int data(int value) { return m_data = value; } //
write property
private:
int m_data;
}
```
In the above example
(https://dlang.org/spec/function.html#property-functions)
@property is placed before the return type of the property and
not after the parameters section.
At first I started to do the same, say, by intuition, but then I
saw lots of examples like:
```d
string something() @property { return this.whatever; }
```
... and changed them accordingly.
Now I am not sure which is the correct way.
Thanks alexandri
Re: Error: function `...` without `this` cannot be `const`
On Wed, Jun 30, 2021 at 05:47:05PM +, someone via Digitalmars-d-learn wrote:
[...]
> ```d
> public string getAmountSI(
>in float lnumAmount
>) const {
[...]
> }
> ```
>
> I used to put all attributes BEFORE the function name which now I
> understand is completely wrong since they should follow the parameter
> declaration section because putting them before affects the function
> in other ways.
The `const` here is being applied to the implicit `this` parameter to
your function. If your function is not a member function (does not have
an implicit `this` parameter), then the attribute is meaningless.
T
--
Give me some fresh salted fish, please.
Re: Error: function `...` without `this` cannot be `const`
On Wednesday, 30 June 2021 at 17:47:05 UTC, someone wrote: ... That is because const/immutable/shared are being applied on the object hence 'this' variable inside function body if function is a member of a struct or class. It doesn't make sense to have a const modifier on a simple function. What will that const mean then in context of that function? To what it will be applied? Best regards, alexandri.
Error: function `...` without `this` cannot be `const`
I do not understand the compiler error when I add the const
keyword in the following function which works (and compiles) as
expected without the const keyword:
```d
public string getAmountSI(
in float lnumAmount
) const {
/// (1) given amount
string lstrAmount;
if (lnumAmount < 1_000f) {
lstrAmount = r"1K"c;
} else {
if (lnumAmount < 1_000_000f) {
lstrAmount = format(r"%.0fK"c, lnumAmount / 1_000f);
} else {
lstrAmount = format(r"%.0fM"c, lnumAmount / 1_000_000f);
}
}
return lstrAmount;
}
```
I used to put all attributes BEFORE the function name which now I
understand is completely wrong since they should follow the
parameter declaration section because putting them before affects
the function in other ways.
I first noted this while browsing the DUB package DB and came
accross https://code.dlang.org/packages/dscanner which states
(among a lot of checks):
- Placement of const, immutable, or inout before a function
return type instead of after the parameters
Is it because const for a function is intended to be used ONLY
within a structure/class (ie: a method) and thus the this error
(http://ddili.org/ders/d.en/const_member_functions.html) ?
Can anyone explain please ?
PS: I think I should re-check all the code I've written so far
for things like this that obviously I quite not completely
understand yet.
Re: float price; if (price == float.nan) { // initialized } else { // uninitialized } ... valid ?
On Wednesday, 30 June 2021 at 16:24:38 UTC, Andre Pany wrote: Side note: in case you want to work with money, you may consider using a specific data type like https://code.dlang.org/packages/money instead of float/double. Yes, I've seen it, and in a previous-unrelated post I commented I am planning to use it (or something similar) because floats and currency are a horrible combo. I am not using it right now because I want to learn the language and encountering situations like this one helps me a lot, otherwise, I would have never noted such NaN behavior -to me, there are a lots of things that could fly under the radar at this moment. And by the way, looking at the code, money seems a quite simple non-nonsense implementation making it a solid candidate :) Thanks for the tip Andre !
Re: float price; if (price == float.nan) { // initialized } else { // uninitialized } ... valid ?
On Wednesday, 30 June 2021 at 03:15:46 UTC, someone wrote:
Is the following code block valid ?
```d
float price; /// initialized as float.nan by default ... right ?
if (price == float.nan) {
/// writeln("initialized");
} else {
/// writeln("uninitialized");
}
```
if so, the following one should be valid too ... right ?
```d
float price;
if (price != float.nan) {
/// writeln("initialized");
}
```
Side note: in case you want to work with money, you may consider
using a specific data type like
https://code.dlang.org/packages/money instead of float/double.
Kind regards
Andre
Re: float price; if (price == float.nan) { // initialized } else { // uninitialized } ... valid ?
On Wednesday, 30 June 2021 at 10:38:05 UTC, jmh530 wrote: You've never given something away for free? ... more often than usual LoL Now, seriously, something for free has not a price = 0, it has NO price, that's what null is for; we use zero for the lack of null.
Re: float price; if (price == float.nan) { // initialized } else { // uninitialized } ... valid ?
On Wednesday, 30 June 2021 at 09:36:34 UTC, Dennis wrote: A `string` is not a class but an array, an `immutable(char)[]`. You're right. My fault.
Re: float price; if (price == float.nan) { // initialized } else { // uninitialized } ... valid ?
On Wednesday, 30 June 2021 at 04:17:19 UTC, someone wrote: On Wednesday, 30 June 2021 at 03:55:05 UTC, Vladimir Panteleev wrote: If you want to give any type a "null" value, you could use [`std.typecons.Nullable`](https://dlang.org/library/std/typecons/nullable.html). At LEAST for some things with currency types like prices which cannot be zero because 0 makes no sense for a price: [snip] You've never given something away for free?
Re: float price; if (price == float.nan) { // initialized } else { // uninitialized } ... valid ?
On Wednesday, 30 June 2021 at 03:52:51 UTC, someone wrote:
at least I can do nulls with strings since it a class :)
A `string` is not a class but an array, an `immutable(char)[]`.
For arrays, `null` is equal to an empty array `[]`.
```D
void main() {
string s0 = null;
string s1 = [];
assert(s0 == s1);
assert(s0.length == 0); // no null dereference here
}
```
