In Dart is there a quick way to convert int to double?

Question

Very simple issue. I have the useless class:

class Useless{
  double field;
  Useless(this.field);
}

I then commit the mortal sin and call new Useless(0); In checked mode (which is how I run my tests) that blows up, because 'int' is not a subtype of type 'double'.

Now, it works if I use new Useless(0.0) , but honestly I spend a lot of time correcting my tests putting .0s everywhere and I feel pretty dumb doing that.

As a temporary measure I rewrote the constructor as:

    class Useless{
      double field;
      Useless(num input){
          field = input.toDouble();
      }
    }

But that's ugly and I am afraid slow if called often. Is there a better way to do this?

Why do you need a double? Can't you just use `num` everywhere? — Robert, Oct 17 '14 at 04:39
Following the Dart style guide: "PREFER using double or int instead of num for parameter type annotations in performance sensitive code" — CarrKnight, Oct 17 '14 at 04:52
This doesnt look like performance sensitive code to me. I think you should decide if you need a general number or if you really need int or double and then you should change all your code to be num, int or double. — Robert, Oct 17 '14 at 06:50
@Robert Using `int` and `double` instead of `num` is better for conveying intention. Why stop at using `num`? We can just make all variables `dynamic` and get rid of all strong typing annoyances in one strike... — obe, Sep 18 '21 at 14:10

Ronen Rabinovici · Answer 1 · 2018-12-23T10:48:26.263

191

Simply toDouble()

Example:

int intVar = 5;
double doubleVar = intVar.toDouble();

Thanks to @jamesdlin who actually gave this answer in a comment to my previous answer...

edited Dec 23 '18 at 10:48

answered Aug 02 '18 at 18:52

Ronen Rabinovici

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jamesdlin · Accepted Answer · 2021-02-06T20:51:39.493

92

In Dart 2.1, integer literals may be directly used where double is expected. (See https://github.com/dart-lang/sdk/issues/34355.)

Note that this is syntactic sugar and applies only to literals. int variables still won't be automatically promoted to double, so code like:

double reciprocal(double d) => 1 / d;

int x = 42;
reciprocal(x);

would fail, and you'd need to do:

reciprocal(x.toDouble());

edited Feb 06 '21 at 20:51

answered Nov 05 '18 at 23:20

jamesdlin

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Mattia · Answer 3 · 2018-09-09T10:32:10.933

46

You can also use:

int x = 15;
double y = x + .0;

edited Sep 09 '18 at 10:32

answered Aug 02 '18 at 19:02

Mattia

5,909
3
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41

1

I found this answer most useful when I wanted to cast from a Map where the value could already be a map: `(map['length'] == null) ? null : map['length'] + .0` – Jannie Theunissen Nov 13 '20 at 07:02
2

i had to do then when parsing HTTP json response. Is there a better way? – alex Dec 11 '21 at 00:41
This is also valid for when you want a const value whereas `.toDouble()` is not – Dave Mackintosh Jan 12 '22 at 22:10

score 18 · Answer 4 · edited Nov 05 '20 at 11:39

18

use toDouble() method.
For e.g.:

int a = 10
print(a.toDouble) 
//or store value in a variable and then use
double convertedValue = a.toDouble()

edited Nov 05 '20 at 11:39

Mangaldeep Pannu

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answered Nov 05 '20 at 11:14

Umar Calcuttawala

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Lebohang Mbele · Answer 5 · 2018-12-17T22:23:59.053

From this attempt:

class Useless{
  double field;
  Useless(num input){
    field = input.toDouble();
  }
}

You can use the parse method of the double class which takes in a string.

class Useless{
  double field;
  Useless(num input){
    field = double.parse(input.toString()); //modified line
  }
}

A more compact way of writing the above class using constructor's initialisers is:

class Useless{
  double _field;
  Useless(double field):_field=double.parse(field.toString());
}

score 5 · Answer 6 · answered Oct 27 '20 at 16:14

5

Since all divisions in flutter result to a double, the easiest thing I did to achieve this was just to divide the integer value with 1: i.e. int x = 15; double y = x /1;

answered Oct 27 '20 at 16:14

Michael Elimu

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3

score 4 · Answer 7 · answered Oct 17 '14 at 05:58

4

There's no better way to do this than the options you included :(

I get bitten by this lots too, for some reason I don't get any warnings in the editor and it just fails at runtime; mighty annoying :(

answered Oct 17 '14 at 05:58

Danny Tuppeny

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score 2 · Answer 8 · answered Jul 06 '20 at 09:32

2

I'm using a combination:

static double checkDouble(dynamic value) {
  if (value is String) {
    return double.parse(value);
  } else if (value is int) {
    return 0.0 + value;
  } else {
    return value;
  }
}

answered Jul 06 '20 at 09:32

Ricardo

2,086
25
35

score 0 · Answer 9 · answered Nov 11 '22 at 13:14

0

This is how you can cast from int to double int a = 2; double b = a*1.0;

answered Nov 11 '22 at 13:14

jordan wilfry

37
3

In Dart is there a quick way to convert int to double?

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