digitalmars.D.learn - How to convert `std.datetime.Duration` to seconds of floating point
Now I do it this way (https://run.dlang.io/is/8kVibT): ``` auto some_duration = dur!"msecs"(500); auto seconds = some_duration.total!"hnsecs" / 10_000_000.0; assert(seconds.approxEqual(0.5)); ``` is there better way to do it? Thanks in advance
Feb 19 2019
On Tuesday, 19 February 2019 at 14:34:09 UTC, drug wrote:Now I do it this way (https://run.dlang.io/is/8kVibT): ``` auto some_duration = dur!"msecs"(500); auto seconds = some_duration.total!"hnsecs" / 10_000_000.0; assert(seconds.approxEqual(0.5)); ``` is there better way to do it?What you're doing now is the way to do it. This is by design, as Jonathan M. Davis explains: "In general, using floating point values with time is an incredibly bad idea. It can certainly make sense when printing stuff out, but using it in calculations is just asking for trouble given all of the unnecessary imprecision that it adds. So, Duration does not directly support floating point values at all, and that's very much on purpose. (...) And if you're just trying to print out the a duration as a floating point value, because it's nice to view that way, then that's fine, but you'll need to do the conversion yourself. And it's not that hard." https://forum.dlang.org/post/mailman.3711.1453121204.22025.digitalmars-d-learn puremagic.com
Feb 19 2019
On 19.02.2019 18:07, Dennis wrote:On Tuesday, 19 February 2019 at 14:34:09 UTC, drug wrote:Well, I understand that using floating point values to represent time internally is a bad idea and I totally agree. But some convenient API to convert Duration to floating point and vice versa would be useful because in mechanics for example you often need to express time in seconds with fractional part. In this regard std::chrono is more expressive (the only one though, in general std.datetime is much more powerful than std::chrono).Now I do it this way (https://run.dlang.io/is/8kVibT): ``` auto some_duration = dur!"msecs"(500); auto seconds = some_duration.total!"hnsecs" / 10_000_000.0; assert(seconds.approxEqual(0.5)); ``` is there better way to do it?What you're doing now is the way to do it. This is by design, as Jonathan M. Davis explains: "In general, using floating point values with time is an incredibly bad idea. It can certainly make sense when printing stuff out, but using it in calculations is just asking for trouble given all of the unnecessary imprecision that it adds. So, Duration does not directly support floating point values at all, and that's very much on purpose. (...) And if you're just trying to print out the a duration as a floating point value, because it's nice to view that way, then that's fine, but you'll need to do the conversion yourself. And it's not that hard." https://forum.dlang.org/post/mailman.3711.1453121204.22025.digitalmars-d learn puremagic.com
Feb 19 2019
On Tuesday, 19 February 2019 at 16:26:33 UTC, drug wrote:Well, I understand that using floating point values to represent time internally is a bad idea and I totally agree. But some convenient API to convert Duration to floating point and vice versa would be useful because in mechanics for example you often need to express time in seconds with fractional part. In this regard std::chrono is more expressive (the only one though, in general std.datetime is much more powerful than std::chrono).If you need a real (double, float) parameter, just use it. Transport the units separately...
Feb 19 2019
On 19.02.2019 19:35, Alex wrote:On Tuesday, 19 February 2019 at 16:26:33 UTC, drug wrote:Could you elaborate what you mean? ``` auto point = vec3(1.0, 2.0, 3.0); vec3 velocity = ...; auto t = dur!"msecs"(500); ... auto new_point = point + velocity * t.total!"msecs"/1e3; ``` How can I use a real parameter and transport units separately here?Well, I understand that using floating point values to represent time internally is a bad idea and I totally agree. But some convenient API to convert Duration to floating point and vice versa would be useful because in mechanics for example you often need to express time in seconds with fractional part. In this regard std::chrono is more expressive (the only one though, in general std.datetime is much more powerful than std::chrono).If you need a real (double, float) parameter, just use it. Transport the units separately...
Feb 19 2019
On Tuesday, 19 February 2019 at 16:44:23 UTC, drug wrote:On 19.02.2019 19:35, Alex wrote:like ´´´ import std.datetime; void main() { import std.stdio; auto d = Data!"msecs"(); writeln(d.point); writeln(d.t); } struct Data(string units) { real[3] point = [1.0, 2.0, 3.0]; real[3] velocity = ...; auto t = dur!units(500); } ´´´On Tuesday, 19 February 2019 at 16:26:33 UTC, drug wrote:Could you elaborate what you mean? ``` auto point = vec3(1.0, 2.0, 3.0); vec3 velocity = ...; auto t = dur!"msecs"(500); ... auto new_point = point + velocity * t.total!"msecs"/1e3; ``` How can I use a real parameter and transport units separately here?Well, I understand that using floating point values to represent time internally is a bad idea and I totally agree. But some convenient API to convert Duration to floating point and vice versa would be useful because in mechanics for example you often need to express time in seconds with fractional part. In this regard std::chrono is more expressive (the only one though, in general std.datetime is much more powerful than std::chrono).If you need a real (double, float) parameter, just use it. Transport the units separately...
Feb 19 2019
drug <drug2004 bk.ru> 19.02.2019 19:55, Alex пишет:On Tuesday, 19 February 2019 at 16:44:23 UTC, drug wrote:Well, your code is more heavy and less flexible than just using `total!"msecs"/1e3`. Sorry, but it's loosely coupled with my question.On 19.02.2019 19:35, Alex wrote:like ´´´ import std.datetime; void main() { import std.stdio; auto d = Data!"msecs"(); writeln(d.point); writeln(d.t); } struct Data(string units) { real[3] point = [1.0, 2.0, 3.0]; real[3] velocity = ...; auto t = dur!units(500); } ´´´On Tuesday, 19 February 2019 at 16:26:33 UTC, drug wrote:Could you elaborate what you mean? ``` auto point = vec3(1.0, 2.0, 3.0); vec3 velocity = ...; auto t = dur!"msecs"(500); ... auto new_point = point + velocity * t.total!"msecs"/1e3; ``` How can I use a real parameter and transport units separately here?Well, I understand that using floating point values to represent time internally is a bad idea and I totally agree. But some convenient API to convert Duration to floating point and vice versa would be useful because in mechanics for example you often need to express time in seconds with fractional part. In this regard std::chrono is more expressive (the only one though, in general std.datetime is much more powerful than std::chrono).If you need a real (double, float) parameter, just use it. Transport the units separately...
Feb 19 2019