Is the following code block valid ?

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 ?

float price;

if (price != float.nan) {

   /// writeln("initialized");

}

On Wednesday, 30 June 2021 at 03:15:46 UTC, someone wrote:

Comparison with nan always results in false:

See section 10.11.5:

https://dlang.org/spec/expression.html#equality_expressions

You can use the is operator to perform bitwise comparison, or use std.math.isNaN.

On Wednesday, 30 June 2021 at 03:32:27 UTC, Vladimir Panteleev wrote:

Side note: That doesn't apply to if (myFloat) or assert(myFloat);, unfortunately: https://issues.dlang.org/show_bug.cgi?id=13489

On Wednesday, 30 June 2021 at 03:32:27 UTC, Vladimir Panteleev wrote:

THAT explains a lot !

missed it.

One of the things I do not like with D, and it causes me to shoot me on the foot over and over, is the lack of null for every data type. Things like:

float lnumStockPricePreceding = null;

foreach (float lnumStockPrice; ludtStockPriceEvolution.range)

   if (lnumStockPricePreceding ! is null) {

      /// do something

   }

   lnumStockPricePreceding = lnumStockPrice;

}

... were first attempted like following on D:

float lnumStockPricePreceding;

foreach (float lnumStockPrice; ludtStockPriceEvolution.range)

   if (lnumStockPricePreceding != float.nan) {

      /// do something

   }

   lnumStockPricePreceding = lnumStockPrice;

}

... and now need to be recoded like:

float lnumStockPricePreceding = 0f;

foreach (float lnumStockPrice; ludtStockPriceEvolution.range)

   if (lnumStockPricePreceding != 0f) {

      /// do something

   }

   lnumStockPricePreceding = lnumStockPrice;

}

... which oftenly complicates things because sometimes even 0f is a valid value for the task at hand and thus I MISS NULLs A LOT :( ... at least I can do nulls with strings since it a class :)

On Wednesday, 30 June 2021 at 03:52:51 UTC, someone wrote:

If you want to give any type a "null" value, you could use std.typecons.Nullable.

On Wednesday, 30 June 2021 at 03:51:47 UTC, Mathias LANG wrote:

import std.math : isNaN;

float lnumStockPricePreceding;

foreach (float lnumStockPrice; ludtStockPriceEvolution.range)

   if (! isNan(lnumStockPricePreceding)) {

      /// do something

   }

   lnumStockPricePreceding = lnumStockPrice;

}

... is far from pretty but it works as expected, thanks for your tip !

On Wednesday, 30 June 2021 at 03:55:05 UTC, Vladimir Panteleev wrote:

Practically Nullable!T stores a T and a bool.

I like the idea :)

On Wednesday, 30 June 2021 at 04:03:24 UTC, someone wrote:

Can be made a bit prettier with UFCS:

import std.math : isNaN;

float lnumStockPricePreceding;

foreach (float lnumStockPrice; ludtStockPriceEvolution.range)

   if (!lnumStockPricePreceding.isNan) {

      /// do something

   }

   lnumStockPricePreceding = lnumStockPrice;

}

Or even better, with ranges:

import std.math : isNaN;

float lnumStockPricePreceding;

foreach (float lnumStockPrice; ludtStockPriceEvolution.range.filter!(f => !f.isNan))
      /// do something

   lnumStockPricePreceding = lnumStockPrice;

}

On Wednesday, 30 June 2021 at 03:55:05 UTC, Vladimir Panteleev wrote:

At LEAST for some things with currency types like prices which cannot be zero because 0 makes no sense for a price:

Nullable!(T, nullValue) is more storage-efficient than Nullable!T because it does not need to store an extra bool.

This could come handly. We'll see.

On Wednesday, 30 June 2021 at 03:52:51 UTC, someone wrote:

A string is not a class but an array, an immutable(char)[]. For arrays, null is equal to an empty array [].

void main() {
    string s0 = null;
    string s1 = [];
    assert(s0 == s1);
    assert(s0.length == 0); // no null dereference here
}