Trait that contains require, and requireState, and requireNonNull methods for checking pre-conditions
that give descriptive error messages extracted via a macro.
These methods of trait Requirements aim to improve error messages provided when a pre-condition check fails at runtime in
production code. Although it is recommended practice to supply helpful error messages when doing pre-condition checks, often people
don't. Instead of this:
scala> val length = 5 length: Int = 5 scala> val idx = 6 idx: Int = 6 scala> require(idx >= 0 && idx <= length, "index, " + idx + ", was less than zero or greater than or equal to length, " + length) java.lang.IllegalArgumentException: requirement failed: index, 6, was less than zero or greater than or equal to length, 5 at scala.Predef$.require(Predef.scala:233) ...
People write simply:
scala> require(idx >= 0 && idx <= length) java.lang.IllegalArgumentException: requirement failed at scala.Predef$.require(Predef.scala:221) ...
Note that the detail message of the IllegalArgumentException thrown by the previous line of code is simply, "requirement failed".
Such messages often end up in a log file or bug report, where a better error message can save time in debugging the problem.
By importing the members of Requirements (or mixing in its companion trait), you'll get a more helpful error message
extracted by a macro, whether or not a clue message is provided:
scala> import org.scalactic._ import org.scalactic._ scala> import Requirements._ import Requirements._ scala> require(idx >= 0 && idx <= length) java.lang.IllegalArgumentException: 6 was greater than or equal to 0, but 6 was not less than or equal to 5 at org.scalactic.Requirements$RequirementsHelper.macroRequire(Requirements.scala:56) ... scala> require(idx >= 0 && idx <= length, "(hopefully that helps)") java.lang.IllegalArgumentException: 6 was greater than or equal to 0, but 6 was not less than or equal to 5 (hopefully that helps) at org.scalactic.Requirements$RequirementsHelper.macroRequire(Requirements.scala:56) ...
The requireState method provides identical error messages to require, but throws
IllegalStateException instead of IllegalArgumentException:
scala> val connectionOpen = false connectionOpen: Boolean = false scala> requireState(connectionOpen) java.lang.IllegalStateException: connectionOpen was false at org.scalactic.Requirements$RequirementsHelper.macroRequireState(Requirements.scala:71) ...
Thus, whereas the require methods throw the Java platform's standard exception indicating a passed argument
violated a precondition, IllegalArgumentException, the requireState methods throw the standard
exception indicating an object's method was invoked when the object was in an inappropriate state for that method,
IllegalStateException.
The requireNonNull method takes one or more variables as arguments and throws NullArgumentException
with an error messages that includes the variable names if any are null. Here's an example:
scala> val e: String = null e: String = null scala> val f: java.util.Date = null f: java.util.Date = null scala> requireNonNull(a, b, c, d, e, f) org.scalactic.exceptions.NullArgumentException: e and f were null at org.scalactic.Requirements$RequirementsHelper.macroRequireNonNull(Requirements.scala:101) ...
Although trait Requirements can help you debug problems that occur in production, bear in mind that a much
better alternative is to make it impossible for such events to occur at all. Use the type system to ensure that all
pre-conditions are met so that the compiler can find broken pre-conditions and point them out with compiler error messages.
When this is not possible or practical, however, trait Requirements is helpful.
Helper class used by code generated by the require macro.
Helper class used by code generated by the require macro.
Require that a boolean condition about an argument passed to a method, function, or constructor,
and described in the given clue, is true.
Require that a boolean condition about an argument passed to a method, function, or constructor,
and described in the given clue, is true.
If the condition is true, this method returns normally.
Else, it throws IllegalArgumentException with the
String obtained by invoking toString on the
specified clue and appending that to the macro-generated
error message as the exception's detail message.
the boolean condition to check as requirement
an objects whose toString method returns a message to include in a failure report.
IllegalArgumentException if the condition is false.
NullPointerException if message is null.
Require that a boolean condition is true about an argument passed to a method, function, or constructor.
Require that a boolean condition is true about an argument passed to a method, function, or constructor.
If the condition is true, this method returns normally.
Else, it throws IllegalArgumentException.
This method is implemented in terms of a Scala macro that will generate an error message. See the main documentation for this trait for examples.
the boolean condition to check as requirement
IllegalArgumentException if the condition is false.
Require that all passed arguments are non-null.
Require that all passed arguments are non-null.
If none of the passed arguments are null, this method returns normally.
Else, it throws NullArgumentException with an error message that includes the name
(as it appeared in the source) of each argument that was null.
arguments to check for null value
NullArgumentException if any of the arguments are null.
Require that a boolean condition about the state of an object on which a method has been
invoked, and described in the given clue, is true.
Require that a boolean condition about the state of an object on which a method has been
invoked, and described in the given clue, is true.
If the condition is true, this method returns normally.
Else, it throws IllegalStateException with the
String obtained by invoking toString on the
specified clue appended to the macro-generated error message
as the exception's detail message.
the boolean condition to check as a requirement
an object whose toString method returns a message to include in a failure report.
IllegalStateException if the condition is false.
NullPointerException if message is null.
Require that a boolean condition is true about the state of an object on which a method has been invoked.
Require that a boolean condition is true about the state of an object on which a method has been invoked.
If the condition is true, this method returns normally.
Else, it throws IllegalStateException.
This method is implemented in terms of a Scala macro that will generate an error message.
the boolean condition to check as requirement
IllegalStateException if the condition is false.
Helper instance used by code generated by macro assertion.