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A parameterized macro is a macro that is able to insert given objects into its expansion. This gives the macro some of the power of a function. As a simple example, in the C programming language, this is a typical macro that is not a parameterized macro, i.e., a parameterless macro: #define PI 3.14159
Procedural macros are Rust functions that run and modify the compiler's input token stream, before any other components are compiled. They are generally more flexible than declarative macros, but are more difficult to maintain due to their complexity.
Microsoft Excel allows both "&" and the function "=CONCATENATE(X,Y)". Rust has the concat! macro and the format! macro, of which the latter is the most prevalent throughout the documentation and examples.
Macro languages may be restricted to acting on specially labeled code regions (pre-fixed with a # in the case of the C preprocessor). Alternatively, they may not, but in this case it is still often undesirable to (for instance) expand a macro embedded in a string literal, so they still need a rudimentary awareness of syntax. That being the case ...
A macro is a piece of code that executes at compile time and either performs textual manipulation of code to-be compiled (e.g. C++ macros) or manipulates the abstract syntax tree being produced by the compiler (e.g. Rust or Lisp macros). Textual macros are notably more independent of the syntax of the language being manipulated, as they merely ...
Line vs. block – a line comment starts with a delimiter and continues to the end of the line (newline marker) whereas a block comment starts with one delimiter and ends with another and can cross lines
A function definition starts with the name of the type of value that it returns or void to indicate that it does not return a value. This is followed by the function name, formal arguments in parentheses, and body lines in braces. In C++, a function declared in a class (as non-static) is called a member function or method.
Each "route" is a rust function with a macro attached to it. The function will define code that should respond to an HTTP request. The macro that is written as part of the function declaration will define which HTTP Method (such as GET, POST, PUT, etc.) it should be handle, as well as a pattern describing the URL it should be relevant to.