Fortran type-free variable and type-free dictionary
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Signed-off-by: Nick Papior <>
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A variable and dictionary in pure fortran for retaining any data-type and a fast hash-table dictionary.


This module consists of two separate modules which co-exist for maintenance and usage reasons.

First, the variable module which is a type-free variable that can contain any variable type, and any dimension as well.

Second, the dictionary module which contains a hash-table of variables that can contain any data-type allowed by the variable module.

Downloading and installation

Installing fdict requires a download of the library hosted at github at fdict@git.

Extract and create an setup.make file for compilation, a minimal setup.make file can look like this


Type make and a library called libfdict.a is created.
Subsequently the installation may be performed by:

make PREFIX=/papth/to/fdict install

which installs the required files (modules and libraries) to the folder.

To use the dictionary you need to add include statements for the modules as well as linking to the program.

To link fdict to your program the following can be used in a Makefile

FDICT_PATH  = /path/to/fdict/parent

Controlling interface parameters

Typically not needed: allows for customization of different interfaces.

By default the number of dimensions allowed by the library is 3, i.e. there is no interface created for real a(:,:,:,:), etc. However, to accomodate arbitrary dimensions you can call a setup script which initializes a different number of dimensions, which can be controlled individually.

Run ./ to get options regarding the setup.

For instance, if you require interfaces for real and real(kind(0.d0)) up to 4 dimensions and all others up to 3 dimensions you can do this

# -A == all data-types, s = single, d = double
./ -A 3 -s 4 -d 4
# -R is a shorthand for both -s and -d
./ -A 3 -R 4


Using this module one gains access to a generic type variable which can contain any data format.

Basically it is used like this:

use variable
integer :: a(3)
type(var) :: v
a = 2
call assign(v,a)
a = 3
call assign(a,v)

Also the variable contains an abbreviation for assigning pointers to not copy data, but retain data locality:

integer, target :: a(3)
type(var) :: v
a = 2
call associate(v,a)
a = 3
! Now v contains a = 3

To delete a variable one simply does:

use variable
type(var) :: v
call delete(v)

However, when the variable is using pointers, instead the user can do

use variable
type(var) :: v
call delete(v,dealloc=.false.)
! or
call nullify(v)

which merely destroys the variable object and thus retains the data where it is. As with any other pointer arithmetic it is up to the programmer to ensure no memory leaks.


Using type(var) it becomes easy to create dictionaries in fortran.

Using this module we implement a dictionary which can contain any data format using a key:val based formalism. The underlying data structure is a linked list sorted according to hash-values of the keys. Hence searching for specific elements in the dictionary is extremely fast. Concatenating dictionaries is also very fast.

Creating a dictionary is almost as easy as the Python equivalent:

use dictionary
type(dict) :: dic
dic = ('KEY'.kv.1)

To extend a dictionary one uses the concatenating format:

dic = dic // ('Hello'.kv.'world') // ('No'.kv.'world')

Again as is used by the type(var) one can with benefit use .kvp. to create the dictionary value by pointers instead of copying the content.
Hence doing:

real :: r(4)
dic = dic // ('reals'.kvp.r)
r = 4

will change the value in the dictionary.

Note that the dictionary can also contain any data type.

However, if it needs to do custom data-types the programmer needs to extend the code by supplying a few custom routines.

Intrinsically the dictionary can contain dictionaries by this:

use dictionary
type(dict) :: d1, d2
d1 = ('hello'.kv.'world')
d2 = ('hello'.kv.'world')
d1 = d1 // ('dict'.kvp.d2)

But it will be up to the user to know the key for data types other than integers, reals, complex numbers and characters.

Note that the dictionary contained is passed by reference, and thus if you delete d2, you will have a dangling pointer in d1.

Contributions, issues and bugs

I would advice any users to contribute as much feedback and/or PRs to further maintain and expand this library.

Please do not hesitate to contribute!

If you find any bugs please form a bug report/issue.

If you have a fix please consider adding a pull request.


The fdict license is MPL-2.0, see the LICENSE file.


A big thanks goes to Alberto Garcia for contributing ideas and giving me bug reports. Without him the interface would have been much more complex!