FormatException

class FormatException implements Exception

Exception thrown when a string or some other data does not have an expected format and cannot be parsed or processed.

Implemented types

• Exception

Constructors

FormatException() const

const FormatException([String message = "", dynamic source, int? offset])

Creates a new FormatException with an optional error message.

Optionally also supply the actual source with the incorrect format, and the offset in the format where a problem was detected.

Implementation

@pragma("vm:entry-point")
const FormatException([this.message = "", this.source, this.offset]);

Properties

hashCode no setter inherited

int get hashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

message final

final String message

A message describing the format error.

Implementation

final String message;

offset final

final int? offset

The offset in source where the error was detected.

A zero-based offset into the source that marks the format error causing this exception to be created. If source is a string, this should be a string index in the range 0 <= offset <= source.length.

If input is a string, the toString method may represent this offset as a line and character position. The offset should be inside the string, or at the end of the string.

May be omitted. If present, source should also be present if possible.

Implementation

final int? offset;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

source final

final dynamic source

The actual source input which caused the error.

This is usually a String, but can be other types too. If it is a string, parts of it may be included in the toString message.

The source is null if omitted or unknown.

Implementation

final dynamic source;

Methods

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toString() override

String toString()

Returns a description of the format exception.

The description always contains the message.

If source is present and is a string, the description will contain (at least a part of) the source. If offset is also provided, the part of the source included will contain that offset, and the offset will be marked.

If the source is a string and it contains a line break before offset, only the line containing offset will be included, and its line number will also be part of the description. Line and character offsets are 1-based.

Implementation

String toString() {
  String report = "FormatException";
  Object? message = this.message;
  if (message != null && "" != message) {
    report = "$report: $message";
  }
  int? offset = this.offset;
  Object? source = this.source;
  if (source is String) {
    if (offset != null && (offset < 0 || offset > source.length)) {
      offset = null;
    }
    &#47;&#47; Source is string and offset is null or valid.
    if (offset == null) {
      if (source.length > 78) {
        source = source.substring(0, 75) + "...";
      }
      return "$report\n$source";
    }
    int lineNum = 1;
    int lineStart = 0;
    bool previousCharWasCR = false;
    for (int i = 0; i < offset; i++) {
      int char = source.codeUnitAt(i);
      if (char == 0x0a) {
        if (lineStart != i || !previousCharWasCR) {
          lineNum++;
        }
        lineStart = i + 1;
        previousCharWasCR = false;
      } else if (char == 0x0d) {
        lineNum++;
        lineStart = i + 1;
        previousCharWasCR = true;
      }
    }
    if (lineNum > 1) {
      report += " (at line $lineNum, character ${offset - lineStart + 1})\n";
    } else {
      report += " (at character ${offset + 1})\n";
    }
    int lineEnd = source.length;
    for (int i = offset; i < source.length; i++) {
      int char = source.codeUnitAt(i);
      if (char == 0x0a || char == 0x0d) {
        lineEnd = i;
        break;
      }
    }
    int length = lineEnd - lineStart;
    int start = lineStart;
    int end = lineEnd;
    String prefix = "";
    String postfix = "";
    if (length > 78) {
      &#47;&#47; Can't show entire line. Try to anchor at the nearest end, if
      &#47;&#47; one is within reach.
      int index = offset - lineStart;
      if (index < 75) {
        end = start + 75;
        postfix = "...";
      } else if (end - offset < 75) {
        start = end - 75;
        prefix = "...";
      } else {
        &#47;&#47; Neither end is near, just pick an area around the offset.
        start = offset - 36;
        end = offset + 36;
        prefix = postfix = "...";
      }
    }
    String slice = source.substring(start, end);
    int markOffset = offset - start + prefix.length;
    return "$report$prefix$slice$postfix\n${" " * markOffset}^\n";
  } else {
    &#47;&#47; The source is not a string.
    if (offset != null) {
      report += " (at offset $offset)";
    }
    return report;
  }
}

Operators

operator ==() inherited

bool operator ==(Object other)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);