How Do Slashes and Dots Facilitate Namespace Separation in Go's C Code?

Interplay of Slashes and Dots in Go's C Code

Within the context of Go's source code, the slashes (∕) and dots (·) found in function names and prototypes hold unique meanings. This deviation from standard C syntax arises from the involvement of the Go Language Suite's internal C compiler, which has roots in the Plan 9 C compiler.

One significant extension introduced by this compiler is the acceptance of UTF-8 characters in identifiers. The middot character (·) acts as a unique element, translating to a regular dot (.) in object files. Notably, Go Language Suite's internal linker then interprets this dot as a namespace separator.

To illustrate this concept, consider the following code snippet from race.c:

<code class="c">void runtime∕race·Read(int32 goid, void *addr, void *pc);
void runtime∕race·Write(int32 goid, void *addr, void *pc);

void
runtime·raceinit(void)
{
    // ...
}</code>

In this context, the middots (·) signify the separation between the runtime namespace (runtime) and the function names (Read, Write, and raceinit). When the compiler translates this code, the object files will contain symbols such as:

T runtime.Read
T runtime.Write
T runtime.raceinit

Interestingly, the "empty" or "placeholder" namespace appears as "". When Go code imports a package using this namespace, the linker replaces the "" with the appropriate path, ensuring the correct symbol resolution during linking.

For instance, if a Go program imports the package "example" with the following code:

<code class="go">import examp "path/to/package/example"

//...

func main() {
    examp.Bar1()
}</code>

The resulting linked program will reveal a symbol like:

T path/to/package/example.Bar1

In summary, the slashes and dots in Go's C code are extensions that facilitate namespace separation and make it possible to access Go functions from regular C code. This unique syntax reflects the underlying implementation of the Go Language Suite and enables the seamless integration of Go code with other languages through C interoperability.

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