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RST backtick refactor (all *.rst except manual.rst and rst_examples.rst) (#17258)

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Co-authored-by: quantimnot <quantimnot@users.noreply.github.com>
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doc/backends.rst
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@ -1,3 +1,5 @@
.. default-role:: code
================================
Nim Backend Integration
================================
@ -13,8 +15,8 @@ Introduction
============
The `Nim Compiler User Guide <nimc.html>`_ documents the typical
compiler invocation, using the ``compile`` or ``c`` command to transform a
``.nim`` file into one or more ``.c`` files which are then compiled with the
compiler invocation, using the `compile` or `c` command to transform a
`.nim` file into one or more `.c` files which are then compiled with the
platform's C compiler into a static binary. However, there are other commands
to compile to C++, Objective-C, or JavaScript. This document tries to
concentrate in a single place all the backend and interfacing options.
@ -23,7 +25,7 @@ The Nim compiler supports mainly two backend families: the C, C++ and
Objective-C targets and the JavaScript target. `The C like targets
<#backends-the-c-like-targets>`_ creates source files that can be compiled
into a library or a final executable. `The JavaScript target
<#backends-the-javascript-target>`_ can generate a ``.js`` file which you
<#backends-the-javascript-target>`_ can generate a `.js` file which you
reference from an HTML file or create a `standalone Node.js program
<http://nodejs.org>`_.
@ -45,7 +47,7 @@ The commands to compile to either C, C++ or Objective-C are:
//compileToOC, objc compile project to Objective C code
The most significant difference between these commands is that if you look
into the ``nimcache`` directory you will find ``.c``, ``.cpp`` or ``.m``
into the `nimcache` directory you will find `.c`, `.cpp` or `.m`
files, other than that all of them will produce a native binary for your
project. This allows you to take the generated code and place it directly
into a project using any of these languages. Here are some typical command-
@ -64,17 +66,17 @@ or compiler/linker commands.
The JavaScript target
---------------------
Nim can also generate `JavaScript`:idx: code through the ``js`` command.
Nim can also generate `JavaScript`:idx: code through the `js` command.
Nim targets JavaScript 1.5 which is supported by any widely used browser.
Since JavaScript does not have a portable means to include another module,
Nim just generates a long ``.js`` file.
Nim just generates a long `.js` file.
Features or modules that the JavaScript platform does not support are not
available. This includes:
* manual memory management (``alloc``, etc.)
* casting and other unsafe operations (``cast`` operator, ``zeroMem``, etc.)
* manual memory management (`alloc`, etc.)
* casting and other unsafe operations (`cast` operator, `zeroMem`, etc.)
* file management
* OS-specific operations
* threading, coroutines
@ -86,14 +88,14 @@ To compensate, the standard library has modules `catered to the JS backend
and more support will come in the future (for instance, Node.js bindings
to get OS info).
To compile a Nim module into a ``.js`` file use the ``js`` command; the
default is a ``.js`` file that is supposed to be referenced in an ``.html``
To compile a Nim module into a `.js` file use the `js` command; the
default is a `.js` file that is supposed to be referenced in an `.html`
file. However, you can also run the code with `nodejs`:idx:
(`<http://nodejs.org>`_)::
nim js -d:nodejs -r examples/hallo.nim
If you experience errors saying that ``globalThis`` is not defined, be
If you experience errors saying that `globalThis` is not defined, be
sure to run a recent version of Node.js (at least 12.0).
@ -113,7 +115,7 @@ Nim code calling the backend
Nim code can interface with the backend through the `Foreign function
interface <manual.html#foreign-function-interface>`_ mainly through the
`importc pragma <manual.html#foreign-function-interface-importc-pragma>`_.
The ``importc`` pragma is the *generic* way of making backend symbols available
The `importc` pragma is the *generic* way of making backend symbols available
in Nim and is available in all the target backends (JavaScript too). The C++
or Objective-C backends have their respective `ImportCpp
<manual.html#implementation-specific-pragmas-importcpp-pragma>`_ and
@ -123,7 +125,7 @@ pragmas to call methods from classes.
Whenever you use any of these pragmas you need to integrate native code into
your final binary. In the case of JavaScript this is no problem at all, the
same HTML file which hosts the generated JavaScript will likely provide other
JavaScript functions which you are importing with ``importc``.
JavaScript functions which you are importing with `importc`.
However, for the C like targets you need to link external code either
statically or dynamically. The preferred way of integrating native code is to
@ -148,7 +150,7 @@ interface.
C invocation example
~~~~~~~~~~~~~~~~~~~~
Create a ``logic.c`` file with the following content:
Create a `logic.c` file with the following content:
.. code-block:: c
int addTwoIntegers(int a, int b)
@ -156,7 +158,7 @@ Create a ``logic.c`` file with the following content:
return a + b;
}
Create a ``calculator.nim`` file with the following content:
Create a `calculator.nim` file with the following content:
.. code-block:: nim
@ -166,26 +168,26 @@ Create a ``calculator.nim`` file with the following content:
when isMainModule:
echo addTwoIntegers(3, 7)
With these two files in place, you can run ``nim c -r calculator.nim`` and
the Nim compiler will compile the ``logic.c`` file in addition to
``calculator.nim`` and link both into an executable, which outputs ``10`` when
With these two files in place, you can run `nim c -r calculator.nim` and
the Nim compiler will compile the `logic.c` file in addition to
`calculator.nim` and link both into an executable, which outputs `10` when
run. Another way to link the C file statically and get the same effect would
be to remove the line with the ``compile`` pragma and run the following typical
be to remove the line with the `compile` pragma and run the following typical
Unix commands::
$ gcc -c logic.c
$ ar rvs mylib.a logic.o
$ nim c --passL:mylib.a -r calculator.nim
Just like in this example we pass the path to the ``mylib.a`` library (and we
could as well pass ``logic.o``) we could be passing switches to link any other
Just like in this example we pass the path to the `mylib.a` library (and we
could as well pass `logic.o`) we could be passing switches to link any other
static C library.
JavaScript invocation example
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Create a ``host.html`` file with the following content:
Create a `host.html` file with the following content:
.. code-block::
@ -199,7 +201,7 @@ Create a ``host.html`` file with the following content:
<script type="text/javascript" src="calculator.js"></script>
</body></html>
Create a ``calculator.nim`` file with the following content (or reuse the one
Create a `calculator.nim` file with the following content (or reuse the one
from the previous section):
.. code-block:: nim
@ -209,9 +211,9 @@ from the previous section):
when isMainModule:
echo addTwoIntegers(3, 7)
Compile the Nim code to JavaScript with ``nim js -o:calculator.js
calculator.nim`` and open ``host.html`` in a browser. If the browser supports
javascript, you should see the value ``10`` in the browser's console. Use the
Compile the Nim code to JavaScript with `nim js -o:calculator.js
calculator.nim` and open `host.html` in a browser. If the browser supports
javascript, you should see the value `10` in the browser's console. Use the
`dom module <dom.html>`_ for specific DOM querying and modification procs
or take a look at `karax <https://github.com/pragmagic/karax>`_ for how to
develop browser-based applications.
@ -222,29 +224,29 @@ Backend code calling Nim
Backend code can interface with Nim code exposed through the `exportc
pragma <manual.html#foreign-function-interface-exportc-pragma>`_. The
``exportc`` pragma is the *generic* way of making Nim symbols available to
`exportc` pragma is the *generic* way of making Nim symbols available to
the backends. By default, the Nim compiler will mangle all the Nim symbols to
avoid any name collision, so the most significant thing the ``exportc`` pragma
avoid any name collision, so the most significant thing the `exportc` pragma
does is maintain the Nim symbol name, or if specified, use an alternative
symbol for the backend in case the symbol rules don't match.
The JavaScript target doesn't have any further interfacing considerations
since it also has garbage collection, but the C targets require you to
initialize Nim's internals, which is done calling a ``NimMain`` function.
initialize Nim's internals, which is done calling a `NimMain` function.
Also, C code requires you to specify a forward declaration for functions or
the compiler will assume certain types for the return value and parameters
which will likely make your program crash at runtime.
The Nim compiler can generate a C interface header through the ``--header``
The Nim compiler can generate a C interface header through the `--header`
command-line switch. The generated header will contain all the exported
symbols and the ``NimMain`` proc which you need to call before any other
symbols and the `NimMain` proc which you need to call before any other
Nim code.
Nim invocation example from C
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Create a ``fib.nim`` file with the following content:
Create a `fib.nim` file with the following content:
.. code-block:: nim
@ -254,7 +256,7 @@ Create a ``fib.nim`` file with the following content:
else:
result = fib(a - 1) + fib(a - 2)
Create a ``maths.c`` file with the following content:
Create a `maths.c` file with the following content:
.. code-block:: c
@ -277,30 +279,30 @@ program::
$ gcc -o m -I$HOME/.cache/nim/fib_d -Ipath/to/nim/lib $HOME/.cache/nim/fib_d/*.c maths.c
The first command runs the Nim compiler with three special options to avoid
generating a ``main()`` function in the generated files, avoid linking the
generating a `main()` function in the generated files, avoid linking the
object files into a final binary, and explicitly generate a header file for C
integration. All the generated files are placed into the ``nimcache``
directory. That's why the next command compiles the ``maths.c`` source plus
all the ``.c`` files from ``nimcache``. In addition to this path, you also
have to tell the C compiler where to find Nim's ``nimbase.h`` header file.
integration. All the generated files are placed into the `nimcache`
directory. That's why the next command compiles the `maths.c` source plus
all the `.c` files from `nimcache`. In addition to this path, you also
have to tell the C compiler where to find Nim's `nimbase.h` header file.
Instead of depending on the generation of the individual ``.c`` files you can
Instead of depending on the generation of the individual `.c` files you can
also ask the Nim compiler to generate a statically linked library::
$ nim c --app:staticLib --noMain --header fib.nim
$ gcc -o m -Inimcache -Ipath/to/nim/lib libfib.nim.a maths.c
The Nim compiler will handle linking the source files generated in the
``nimcache`` directory into the ``libfib.nim.a`` static library, which you can
`nimcache` directory into the `libfib.nim.a` static library, which you can
then link into your C program. Note that these commands are generic and will
vary for each system. For instance, on Linux systems you will likely need to
use ``-ldl`` too to link in required dlopen functionality.
use `-ldl` too to link in required dlopen functionality.
Nim invocation example from JavaScript
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Create a ``mhost.html`` file with the following content:
Create a `mhost.html` file with the following content:
.. code-block::
@ -311,7 +313,7 @@ Create a ``mhost.html`` file with the following content:
</script>
</body></html>
Create a ``fib.nim`` file with the following content (or reuse the one
Create a `fib.nim` file with the following content (or reuse the one
from the previous section):
.. code-block:: nim
@ -322,10 +324,10 @@ from the previous section):
else:
result = fib(a - 1) + fib(a - 2)
Compile the Nim code to JavaScript with ``nim js -o:fib.js fib.nim`` and
open ``mhost.html`` in a browser. If the browser supports javascript, you
should see an alert box displaying the text ``Fib for 9 is 34``. As mentioned
earlier, JavaScript doesn't require an initialization call to ``NimMain`` or
Compile the Nim code to JavaScript with `nim js -o:fib.js fib.nim` and
open `mhost.html` in a browser. If the browser supports javascript, you
should see an alert box displaying the text `Fib for 9 is 34`. As mentioned
earlier, JavaScript doesn't require an initialization call to `NimMain` or
a similar function and you can call the exported Nim proc directly.
@ -335,14 +337,14 @@ Nimcache naming logic
The `nimcache`:idx: directory is generated during compilation and will hold
either temporary or final files depending on your backend target. The default
name for the directory depends on the used backend and on your OS but you can
use the ``--nimcache`` `compiler switch
use the `--nimcache` `compiler switch
<nimc.html#compiler-usage-commandminusline-switches>`_ to change it.
Memory management
=================
In the previous sections, the ``NimMain()`` function reared its head. Since
In the previous sections, the `NimMain()` function reared its head. Since
JavaScript already provides automatic memory management, you can freely pass
objects between the two languages without problems. In C and derivate languages
you need to be careful about what you do and how you share memory. The
@ -357,15 +359,15 @@ Strings and C strings
The manual mentions that `Nim strings are implicitly convertible to
cstrings <manual.html#types-cstring-type>`_ which makes interaction usually
painless. Most C functions accepting a Nim string converted to a
``cstring`` will likely not need to keep this string around and by the time
`cstring` will likely not need to keep this string around and by the time
they return the string won't be needed anymore. However, for the rare cases
where a Nim string has to be preserved and made available to the C backend
as a ``cstring``, you will need to manually prevent the string data from being
as a `cstring`, you will need to manually prevent the string data from being
freed with `GC_ref <system.html#GC_ref,string>`_ and `GC_unref
<system.html#GC_unref,string>`_.
A similar thing happens with C code invoking Nim code which returns a
``cstring``. Consider the following proc:
`cstring`. Consider the following proc:
.. code-block:: nim
@ -373,8 +375,8 @@ A similar thing happens with C code invoking Nim code which returns a
result = "Hey there C code! " & $rand(100)
Since Nim's garbage collector is not aware of the C code, once the
``gimme`` proc has finished it can reclaim the memory of the ``cstring``.
However, from a practical standpoint, the C code invoking the ``gimme``
`gimme` proc has finished it can reclaim the memory of the `cstring`.
However, from a practical standpoint, the C code invoking the `gimme`
function directly will be able to use it since Nim's garbage collector has
not had a chance to run *yet*. This gives you enough time to make a copy for
the C side of the program, as calling any further Nim procs *might* trigger
@ -397,14 +399,14 @@ Again, if you are wrapping a library which *mallocs* and *frees* data
structures, you need to expose the appropriate *free* function to Nim so
you can clean it up. And of course, once cleaned you should avoid accessing it
from Nim (or C for that matter). Typically C data structures have their own
``malloc_structure`` and ``free_structure`` specific functions, so wrapping
`malloc_structure` and `free_structure` specific functions, so wrapping
these for the Nim side should be enough.
Thread coordination
-------------------
When the ``NimMain()`` function is called Nim initializes the garbage
When the `NimMain()` function is called Nim initializes the garbage
collector to the current thread, which is usually the main thread of your
application. If your C code later spawns a different thread and calls Nim
code, the garbage collector will fail to work properly and you will crash.