Crate devela_macros 

A development substrate of coherence.

Procedural macros for devela.

Conditional compilation

Each form of conditional compilation takes a compilation predicate that evaluates to true or false.

These are the #[compile] and #[compile_attr] attributes and the cif! macro.

They are similar to the #[cfg] and #[cfg_attr] attributes and the cfg! macro, except they use compilation predicates.

Panics

Compilation macros will panic if they encounter an unrecognized predicate. As opposed to configuration macros (cfg!) that return false for unrecognized predicates without signaling an error.

Compilation predicates

The following compilation predicates are supported:

• unary:

  • A bare predicate returns true only if it is the true literal.
  • A bare predicate returns false if it’s the false literal or it’s empty.
  • not(): returns true only if the predicate does not evaluate to true.

• binary:

  • equal(): returns true if both predicates are evaluated as equal.

  • xor(): returns true if only one predicate is true, but not both.

  • eq(): returns true if both predicates are number literals and Left == Right.

  • ne(): returns true if both predicates are number literals and Left != Right.

  • ge(): returns true if both predicates are number literals and Left >= Right.

  • gt(): returns true if both predicates are number literals and Left > Right.

  • le(): returns true if both predicates are number literals and Left <= Right.

  • lt(): returns true if both predicates are number literals and Left < Right.

• non-binary:

  • any(): returns true if any predicate is true.
  • all(): returns true if all predicates are true.
  • none(): returns true if there is no given predicate.
  • some(): returns true if there is some given predicate.
  • same(): returns true if all the predicates have the same text.
  • diff(): returns true if any predicate differs from the first in text.
  • nota(): returns true if the first predicate’s text matches none of the additional predicates.
  • xany(): returns true if there are any true predicates, but not all.
  • xodd(): returns true if there is an odd number of true predicates.
  • xone(): returns true if there is just one true predicate, but no more.

• pointer width:

  • pointer_width_eq(width): returns true if current pointer width == the given width.
  • pointer_width_ne(width): returns true if current pointer width != the given width.
  • pointer_width_ge(width): returns true if current pointer width >= the given width.
  • pointer_width_gt(width): returns true if current pointer width > the given width.
  • pointer_width_le(width): returns true if current pointer width <= the given width.
  • pointer_width_lt(width): returns true if current pointer width < the given width.

• endianness:

  • little_endian(): returns true if current architecture is little-endian.
  • big_endian(): returns true if current architecture is big-endian.

• environment variables:

  • env(NAME): returns true if the env var exists.
  • env_eq(NAME, VALUE): returns true if the env var exists and its value == VALUE.
  • env_ne(NAME, VALUE): returns true if the env var exists and its value != VALUE.
  • env_empty(NAME): returns true if the env var exists and its value is empty.
  • env_nonempty(NAME): returns true if the env var exists and its value is non-empty.

Notes

• When more than one predicate is supported, they are separated by commas.
• Env predicates compare textual values, not numeric or boolean coercions.

Empty-argument semantics:

• all() == true
• any() == false
• same() == true
• diff() == false
• none() == true
• some() == false
• nota() == panic (no reference predicate)

Macros

cif

Evaluates to either a true of false literal based on the predicate.

coalesce

Returns the first non-empty argument.

enumint

Generates a unit-only enum with variants associated to a specified range.

field_of

Generates an expression for accessing a field of a tuple or struct.

ident_total

Returns the total number of identifiers in its input.

ident_total_unique

Returns the numbers of both total and unique identifiers in its input.

ident_unique

Returns the number of unique identifiers in its input.

repeat

Repeats an expression the given number of times, as duplicated code with no loops.

Attribute Macros

compile

Conditionally compiles the thing it is attached to based on the predicate.

compile_attr

Conditionally compiles the given attributes based on the predicate.