Declare_parameter in Dashing

[jdlangs]

@wjwwood

I suppose it is unfortunate, but you can also just always do something like get_parameter<string>("something") (pseudo code) and it will either: give you a string, throw because the type is not a string, or throw because it’s not declared. So if you’re ok with an exception for not being declared, can’t you just lean on the exception when it’s not set (and therefore cannot be coerced into a string) as well?

Yes, this seems a reasonable option to use the template argument to force the type conversion. Though it doesn’t look like there currently is a templated version that returns the value.

@wjwwood

I don’t recommend it, however. I don’t understand the need in most cases for using anything but a single declare parameter, as it returns the value just like get parameter does in most cases.

If you don’t expect the parameter to change during runtime, you can just do something like this in your main function or constructor:

auto scalar = node->declare_parameter<double>("some_scalar");
// ...
if (scalar > ...) ...
// ...
printf("some_scalar is: %s\n", std::to_string(scalar).c_str());
// etc...

And you never need to use get_parameter.

Agreed this is reasonable, but again this particular usage doesn’t seem to exist currently in rclcpp (it requires a default value).

Taking a step back though, I trust you can sympathize if I express some frustration that in the end you’re suggesting my code doesn’t need to change except I should rewrite get_parameter as declare_parameter. If for “most cases” that’s all that’s needed, what problem is being solved here? It’s still get_parameter, just now with a name with a less obvious meaning.