gistfile1.txt

    public static Double getNumericValueFromLiteralExpr(GoExpr expr) {
        if (expr instanceof GoLiteralExpression){
            GoLiteral literal = ((GoLiteralExpression) expr).getLiteral();
            if (literal instanceof GoLiteralIdentifier){
                if (((GoLiteralIdentifier) literal).isIota()){
                    Integer iotaValue = ((GoLiteralIdentifier) literal).getIotaValue();
                    if (iotaValue != null)
                        return iotaValue.doubleValue();

                } else {
                    PsiElement goConstIdentifier = GoUtil.ResolveReferece(literal);
                    PsiElement goConstSpec = goConstIdentifier.getParent();
                    if (goConstSpec instanceof GoConstDeclaration) {
                        GoExpr goConstExpr = ((GoConstDeclaration) goConstSpec).getExpression((GoLiteralIdentifier) goConstIdentifier);
                        if (goConstExpr != null)
                            return getNumericValueFromLiteralExpr(goConstExpr);
                    }
                }
            }
            if (literal instanceof GoLiteralInteger) {
                Integer value = ((GoLiteralInteger) literal).getValue();
                return value.doubleValue();
            }
            if (literal instanceof GoLiteralFloat) {
                Float value = ((GoLiteralFloat) literal).getValue();
                return value.doubleValue();
            }
            if (literal.getNode().getElementType() == GoElementTypes.LITERAL_CHAR){
                Integer value = GoPsiUtils.getRuneValue(literal.getText());
                if (value != null){
                    return value.doubleValue();
                }

            }

        }
        if (expr instanceof GoBinaryExpression){
            GoExpr leftOp = ((GoBinaryExpression) expr).getLeftOperand();
            GoExpr rightOp = ((GoBinaryExpression) expr).getRightOperand();
            IElementType op = ((GoBinaryExpression) expr).getOperator();
            if (op == GoElementTypes.oPLUS || op == GoElementTypes.oMINUS
                    || op == GoElementTypes.oMUL || op == GoElementTypes.oQUOTIENT
                    || op == GoElementTypes.oSHIFT_LEFT || op == GoElementTypes.oSHIFT_RIGHT){
                Double leftVal = getNumericValueFromLiteralExpr(leftOp);
                if (leftVal != null){
                    Double rightVal = getNumericValueFromLiteralExpr(rightOp);
                    if (rightVal != null){
                        if (op == GoElementTypes.oPLUS)
                            return leftVal + rightVal;
                        if (op == GoElementTypes.oMINUS)
                            return leftVal - rightVal;
                        if (op == GoElementTypes.oMUL)
                            return leftVal * rightVal;
                        if (op == GoElementTypes.oQUOTIENT && rightVal != 0)
                            return leftVal / rightVal;
//                        if (op == GoElementTypes.oSHIFT_LEFT)
//                            return leftVal << rightVal;
//                        if (op == GoElementTypes.oSHIFT_RIGHT)
//                            return leftVal >> rightVal;
                    }
                }
            }
        }
        if (expr instanceof GoUnaryExpression){
            GoUnaryExpression.Op unaryOp = ((GoUnaryExpression) expr).getUnaryOp();
            GoExpr unaryExpr = ((GoUnaryExpression) expr).getExpression();
            if (unaryOp == GoUnaryExpression.Op.None || unaryOp == GoUnaryExpression.Op.Plus
                    || unaryOp == GoUnaryExpression.Op.Minus || unaryOp == GoUnaryExpression.Op.Xor) {
                Double unaryVal = getNumericValueFromLiteralExpr(unaryExpr);
                if (unaryVal != null) {
                    if (unaryOp == GoUnaryExpression.Op.Minus){
                        return -unaryVal;
                    }
//                    if (unaryOp == GoUnaryExpression.Op.Xor){
//                        unaryVal = ~unaryVal;
//                    }
                }
                return unaryVal;
            }
        }
        if (expr instanceof GoParenthesisedExpression)
            return getNumericValueFromLiteralExpr(((GoParenthesisedExpression) expr).getInnerExpression());
        return null;
    }