I brought up f-strings in another topic where @urbanjost answered and showed a very impressive way to produce very similar behavior with Fortran.
I finally had some spare time to play around and started thinking that what about “replace”. There is a very old issue at (still open) Replace substring in character/string_type · Issue #366 · fortran-lang/stdlib · GitHub. I would be nice to have such feature.
I also started wondering could one do something fun with operators. Here is something that I built on top of @urbanjost 's example in the other thread:
program main
implicit none
integer :: i
real :: a
character(len=:),allocatable :: text
character(len=4096) :: line
character(len=*),parameter :: asis='(*(g0))'
type :: string_replace_t
character(len=4096) :: str
character(len=4096) :: replaced_substr
end type
type(string_replace_t) :: replacable
interface operator(.replace.)
procedure create_replace_type
end interface
interface operator(.with.)
procedure replace_type_with
end interface
i=1
a=1.123456789
text="this"
!py!print(f"{i} is an integer, {a:1.2f} is a rounded real and '{text}' is text")
print asis,i," is an integer, ",fmt(a,'f0.2')," is a rounded real and '",text,"' is text"
! put it into a string with internal write
write(line,asis)i," is an integer, ",fmt(a,'f0.2')," is a rounded real and '",text,"' is text"
call doop(trim(line)) ! do something with line
! concatenation works too and can be passed as an argument, so more compact in some cases
print asis,fmt(i)//" is an integer, "//fmt(a,'f0.2')//" is a rounded real and '"//text//"' is text"
line=fmt(i)//" is an integer, "//fmt(a,'f0.2')//" is a rounded real and '"//text//"' is text"
! replace can be done with operators
line = line.replace."text".with."other text"
print asis, trim(line)
! other example:
print asis,fmt(i)//" is an integer, "//fmt(a,'f0.2')//" is a rounded real and '"//&
text//"' is text".replace."is a rounded real".with."IS A ROUNDED REAL"
contains
function create_replace_type(str, replaced_substr) result (sout)
character(len=*), intent(in) :: str, replaced_substr
type(string_replace_t) :: sout
sout % str = str
sout % replaced_substr = replaced_substr
end function create_replace_type
function replace_type_with(string_replace, with_str) result (sout)
type(string_replace_t), intent(in) :: string_replace
character(len=*), intent(in) :: with_str
character(len=:), allocatable :: sout
integer :: i, rstart, rend
rstart = 0
match_loop: do i = 1, len_trim(string_replace % str)
if (rstart == 0 .and. string_replace % str(i:i) == string_replace % replaced_substr(1:1)) then
rstart = i
else if (rstart > 0 .and. len_trim(with_str)==i-rstart+1) then
rend = i
exit match_loop
else if (rstart > 0 .and. string_replace % str(i:i) /= string_replace % replaced_substr(i-rstart+1:i-rstart+1)) then
rstart = 0
end if
end do match_loop
sout = string_replace % str(1:rstart-1) // with_str // string_replace % str(rend+1:len_trim(string_replace % str))
end function replace_type_with
subroutine doop(string) ! do some operation on string
character(len=*),intent(in) :: string
integer :: i
write(*,asis)(string(i:i),i=len(string),1,-1)
end subroutine doop
recursive function fmt(generic,format) result (line)
use,intrinsic :: iso_fortran_env, only : int8, int16, int32, int64, real32, real64, real128
! ident_4="@(#) M_framework__msg fmt(3f) convert any intrinsic to a string using specified format"
class(*),intent(in) :: generic
character(len=*),intent(in),optional :: format
character(len=:),allocatable :: line
character(len=:),allocatable :: fmt_local
integer :: ios
character(len=255) :: msg
character(len=1),parameter :: null=char(0)
integer :: ilen
if(present(format))then
fmt_local=format
else
fmt_local=''
endif
! add ",a" and print null and use position of null to find length of output
! add cannot use SIZE= or POS= or ADVANCE='NO' on WRITE() on INTERNAL READ,
! and do not want to trim as trailing spaces can be significant
if(fmt_local == '')then
select type(generic)
type is (integer(kind=int8)); fmt_local='(i0,a)'
type is (integer(kind=int16)); fmt_local='(i0,a)'
type is (integer(kind=int32)); fmt_local='(i0,a)'
type is (integer(kind=int64)); fmt_local='(i0,a)'
type is (real(kind=real32)); fmt_local='(1pg0,a)'
type is (real(kind=real64)); fmt_local='(1pg0,a)'
type is (real(kind=real128)); fmt_local='(1pg0,a)'
type is (logical); fmt_local='(l1,a)'
type is (character(len=*)); fmt_local='(a,a)'
type is (complex); fmt_local='("(",1pg0,",",1pg0,")",a)'
end select
else
if(format(1:1) == '(')then
fmt_local=format(:len_trim(format)-1)//',a)'
else
fmt_local='('//fmt_local//',a)'
endif
endif
allocate(character(len=256) :: line) ! cannot currently write into allocatable variable
ios=0
select type(generic)
type is (integer(kind=int8)); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (integer(kind=int16)); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (integer(kind=int32)); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (integer(kind=int64)); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (real(kind=real32)); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (real(kind=real64)); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (real(kind=real128)); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (logical); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (character(len=*)); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
type is (complex); write(line,fmt_local,iostat=ios,iomsg=msg) generic,null
end select
if(ios /= 0)then
line='<ERROR>'//trim(msg)
else
ilen=index(line,null,back=.true.)
if(ilen == 0)ilen=len(line)
line=line(:ilen-1)
endif
end function fmt
end program main
So basically one can now do things like "some string".replace."some".with."A". It might not be super efficient but looks pretty neat. Maybe I am not the only one who thought of it. Has anyone else created such things? I’d be interested.
