Add cpprestsdk options for underlying implementation

[garethsb]

Add Conan options for C++ REST SDK, equivalent to its CMake cache variables, CPPREST_PPLX_IMPL, CPPREST_HTTP_CLIENT_IMPL, CPPREST_HTTP_LISTENER_IMPL, which each support two different values on the Windows platform.

I studied the documentation for config_options and read related issues such as conan-io/conan#3519, since I originally planned to only add these options for some platforms (so that other platforms report exception) and/or add platform-specific default values in config_options, but that didn't seem to work as I expected, so I followed the doc example of removing the options on other platforms instead.

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

[conan-center-bot]

All green in build 1 (bdad34b6c40b083790a02b198b641e95ae789d50)! 😊

• cpprestsdk/2.10.15: Generated 130 packages. All logs here
• cpprestsdk/2.10.16: Generated 130 packages. All logs here

[garethsb]

Since the default values above only apply on Windows, would it be better to remove "pplx_impl": "win", etc. from default_options and in config_options replace the else with the following code under the if self.settings.os == "Windows": branch?

            if self.options.get_safe("pplx_impl") == None:
                self.options["pplx_impl"] = "win"
            if self.options.get_safe("http_client_impl") == None:
                self.options["http_client_impl"] = "winhttp"
            if self.options.get_safe("http_listener_impl") == None:
                self.options["http_listener_impl"] = "httpsys"

[uilianries]

You can't remove default options, Conan will break when building.

It can be improved:

if self.options.get_safe("http_listener_impl") == None:
    self.options["http_listener_impl"] = "httpsys"

if not self.options.get_safe("http_listener_impl"):
    self.options["http_listener_impl"] = "httpsys"

[garethsb]

@uilianries

You can't remove default options, Conan will break when building.

I read this: https://docs.conan.io/en/latest/reference/conanfile/attributes.html#default-options which says "You can also set the options conditionally to a final value with config_options() instead of using default_options". I was asking if that would be more appropriate here?

[uilianries]

You can remove self.options, not self.default_options.

[uilianries]

Almost good, only simplify cmake definitions

[uilianries]

Suggested change

	if self.options.get_safe("pplx_impl"):
	self._cmake.definitions["CPPREST_PPLX_IMPL"] = self.options.pplx_impl
	if self.options.get_safe("http_client_impl"):
	self._cmake.definitions["CPPREST_HTTP_CLIENT_IMPL"] = self.options.http_client_impl
	if self.options.get_safe("http_listener_impl"):
	self._cmake.definitions["CPPREST_HTTP_LISTENER_IMPL"] = self.options.http_listener_impl
	self._cmake.definitions["CPPREST_PPLX_IMPL"] = self.options.get_safe("pplx_impl", False)
	self._cmake.definitions["CPPREST_HTTP_CLIENT_IMPL"] = self.options.get_safe("http_client_impl", False)
	self._cmake.definitions["CPPREST_HTTP_LISTENER_IMPL"] = self.options.get_safe("http_listener_impl", False)

[garethsb]

I don't think that has the same effect? I don't want to set the CMake definitions if the Conan option is not specified.

[uilianries]

Same effect, but simplified. Setting to False is not a problem, if you are following the correct default options.

[madebr]

@uilianries
These options are no bools