plus_months function of the DateLike trait

[dmitriibundin]

Is there a way to add some number of months to NaiveDate? I'm looking for something with the following behavior

assert_eq!(NaiveDate::from_ymd(2015,  1,  5).add_months(10), Some(NaiveDate::from_ymd(2015,  11,  5)));
assert_eq!(NaiveDate::from_ymd(2015,  1,  31).add_months(1), None);

Is it currently implemented somewhere?

[quodlibetor]

Unfortunately not, the closest you can get is adding days or durations.

[doivosevic]

+1 on this and probably related to #52

Would be nice to be able to get last month

[zwq1792966796]

use chrono::{ Datelike, NaiveDate, ParseResult};
fn main() {

let fmt = "%Y-%m-%d";
//

let str_date: String = "2020-12-1".to_string(); // 2021-01-04 20:02:09
println!("now: {}", str_date);
//
let result: ParseResult<NaiveDate> = NaiveDate::parse_from_str(str_date.as_str(), fmt);
if result.is_err() {
    result.expect("parse error");
}
let date: NaiveDate = result.unwrap();


println!("time: {}, parsed from:'{}'", date, str_date);

println!("{}",year_add(&date,1));
println!("{}",month_add(&date,11));
//

println!("{}",-5/12);
println!("{}",-5%12);

let mut v=vec![];
let t=["2020-1-1",
    "2020-1-31",
    "2020-2-1",
    "2020-2-29",
    "2020-3-1",
    "2020-3-31",
    "2020-4-1",
    "2020-4-30",
    "2020-5-1",
    "2020-5-31",
    "2020-6-1",
    "2020-6-30",
    "2020-7-1",
    "2020-7-31",
    "2020-8-1",
    "2020-8-31",
    "2020-9-1",
    "2020-9-30",
    "2020-10-1",
    "2020-10-31",
    "2020-11-1",
    "2020-11-30",
    "2020-12-1",
    "2020-12-31",
];
for i in &t {
    let result: ParseResult<NaiveDate> = NaiveDate::parse_from_str(i, fmt);
    if result.is_err() {
        result.expect("parse error");
        break;
    }
    let date: NaiveDate = result.unwrap();
    v.push(date);
}
for i in v.iter() {
    //println!("{}",i);
    for j in  -48..=48 {
        println!("{}+{}====={}",i.to_string(),j,month_add(i,j));
    }
    println!("======================================")
}

}

fn year_add(date:&NaiveDate,i:i32)->String {
let month=date.month();
let day=date.day();
//is_leap_year(date.year())
match is_leap_year(date.year()) {
true=>match is_leap_year(date.year()+i){
true=>{
format!("{}-{}-{}",date.year()+i,month,day)
},
false=>{
if month==2&&day==29 {
format!("{}-{}-{}",date.year()+i,month,day-1)
}else{
format!("{}-{}-{}",date.year()+i,month,day)
}

        }
    },
    false=>match is_leap_year(date.year()+i){
        true=>{
            if month==2&&day==28 {
                format!("{}-{}-{}",date.year()+i,month,day+1)
            }else{
                format!("{}-{}-{}",date.year()+i,month,day)
            }
        },
        false=>{
            format!("{}-{}-{}",date.year()+i,month,day)  
        }
    }
} 

}
fn is_leap_year(year:i32)->bool{
match year%100{
0=>match year%400{
0=>true,
_=>false,

    },
    _=>match year%4{
        0=>true,
        _=>false           
    }
}

}

fn month_add(date:&NaiveDate,i:i32)->String {
//
let year=date.year() as i32;
let month=date.month() as i32;
let day=date.day() as i32;
// if i==0 {
// date.format("%Y-%m-%d").to_string()
// }else if i>0{
// is_positive(year,month,day,i)
// }else {
// is_negative(year,month,day,i)
// }
if i==0 {
format!("{}-{}-{}",year,month,day)
}else {
let dest_year=year+(month+i)/12;
let dest_month=(month+i)%12;
match dest_month{
0=>{
format!("{}-{}-{}",dest_year-1,12,day)
},
-2|-4|-5|-7|-9|-11=>{
format!("{}-{}-{}",dest_year-1,12+dest_month,day)
},
-1|-3|-6|-8=>{
match day {
31=>{format!("{}-{}-{}",dest_year-1,12+dest_month,30)},
_=>{format!("{}-{}-{}",dest_year-1,12+dest_month,day)},
}
},
-10=>{
match day {
29|30|31=>{
if is_leap_year(dest_year-1){
format!("{}-{}-{}",dest_year-1,12+dest_month,29)
}else {
format!("{}-{}-{}",dest_year-1,12+dest_month,28)
}
},
_=>{format!("{}-{}-{}",dest_year-1,12+dest_month,day)},
}
},
1|3|5|7|8|10=>{
format!("{}-{}-{}",dest_year,dest_month,day)
},
2=>{
if is_leap_year(dest_year) {
match day {
29|30|31=>{
format!("{}-{}-{}",dest_year,dest_month,29)
},
_=>{
format!("{}-{}-{}",dest_year,dest_month,day)
},
}
}else {
match day {
29|30|31=>{
format!("{}-{}-{}",dest_year,dest_month,28)
},
_=>{
format!("{}-{}-{}",dest_year,dest_month,day)
},
}
}
},
4|6|9|11=>{
match day {
31=>format!("{}-{}-{}",dest_year,dest_month,30),
_=>format!("{}-{}-{}",dest_year,dest_month,day)
}
},
_=>{"error".to_string()},
}
}

}

[esheppa]

@doivosevic and @dmitriibundin - I know it's been a while, but does #731 solve your use case?

[pitdicker]

Added in #731.