Maps in Co-array Fortran

To create and manipulate maps in co-array Fortran, you can utilize derived types and procedures. Here’s an example of how this can be done:

module map_module

    implicit none

    type :: map_item
        character(len=:), allocatable :: key
        integer :: value
    end type map_item

    type :: map
        type(map_item), allocatable :: items(:)
    contains
        procedure :: add => add_to_map
        procedure :: get => get_from_map
        procedure :: remove => remove_from_map
        procedure :: size => map_size
        procedure :: clear => clear_map
    end type map

contains

    subroutine add_to_map(this, key, value)
        class(map), intent(inout) :: this
        character(len=*), intent(in) :: key
        integer, intent(in) :: value
        type(map_item) :: new_item

        new_item%key = key
        new_item%value = value

        if (.not. allocated(this%items)) then
            allocate(this%items(1))
            this%items(1) = new_item
        else
            this%items = [this%items, new_item]
        endif
    end subroutine add_to_map

    integer function get_from_map(this, key, found)
        class(map), intent(in) :: this
        character(len=*), intent(in) :: key
        logical, intent(out) :: found
        integer :: i

        found = .false.
        get_from_map = 0

        do i = 1, size(this%items)
            if (this%items(i)%key == key) then
                get_from_map = this%items(i)%value
                found = .true.
                return
            endif
        end do
    end function get_from_map

    subroutine remove_from_map(this, key)
        class(map), intent(inout) :: this
        character(len=*), intent(in) :: key
        integer :: i

        do i = 1, size(this%items)
            if (this%items(i)%key == key) then
                this%items(i:) = this%items(i+1:)
                allocate(this%items(size(this%items)-1))
                return
            endif
        end do
    end subroutine remove_from_map

    integer function map_size(this)
        class(map), intent(in) :: this
        if (allocated(this%items)) then
            map_size = size(this%items)
        else
            map_size = 0
        endif
    end function map_size

    subroutine clear_map(this)
        class(map), intent(inout) :: this
        if (allocated(this%items)) deallocate(this%items)
    end subroutine clear_map
end module map_module

To use the map type, you can write a program as follows:

program main
    use map_module
    implicit none

    type(map) :: m
    integer :: val
    logical :: found

    ! Add elements to the map
    call m%add("k1", 7)
    call m%add("k2", 13)

    ! Print the map size
    print *, "len:", m%size()

    ! Get a value
    val = m%get("k1", found)
    if (found) then
        print *, "v1:", val
    else
        print *, "v1: not found"
    endif

    ! Attempt to get a value for a non-existent key
    val = m%get("k3", found)
    if (found) then
        print *, "v3:", val
    else
        print *, "v3:", val, "(default zero value)"
    endif

    ! Remove an element from the map
    call m%remove("k2")
    print *, "len after remove:", m%size()

    ! Clear the map
    call m%clear()
    print *, "len after clear:", m%size()
end program main

This example defines a map type with add, get, remove, size, and clear methods, similar to the ones in the original example. Note that Fortran does not directly support maps, so an array of derived types is used to simulate map behavior.

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Maps in Co-array Fortran