public static <T extends Expression> T getExpression(Statement stat, Class<T> type) {
    ExpressionStatement exprStat = ObjectUtil.asInstance(stat, ExpressionStatement.class);
    if (exprStat == null) return null;
    return ObjectUtil.asInstance(exprStat.getExpression(), type);
  }
Checks whether the given statement represents a data table separator.
A data table separator is an expression statement consisting of a
variable expression whose name is two or more underscores and
that does not reference any existing variable, parameter or field.

@param stat the statement to check for being a data table separator
@return whether the given statement is a data table separator
spock-core/src/main/java/org/spockframework/compiler/AstUtil.java