function genValuePartial_fromObject(gen, field, fieldIndex, prop) {
    /* eslint-disable no-unexpected-multiline, block-scoped-var, no-redeclare */
    if (field.resolvedType) {
        if (field.resolvedType instanceof Enum) { gen
            ("switch(d%s){", prop);
            for (var values = field.resolvedType.values, keys = Object.keys(values), i = 0; i < keys.length; ++i) {
                if (field.repeated && values[keys[i]] === field.typeDefault) gen
                ("default:");
                gen
                ("case%j:", keys[i])
                ("case %j:", values[keys[i]])
                    ("m%s=%j", prop, values[keys[i]])
                    ("break");
            } gen
            ("}");
        } else gen
            ("if(typeof d%s!==\"object\")", prop)
                ("throw TypeError(%j)", field.fullName + ": object expected")
            ("m%s=types[%d].fromObject(d%s)", prop, fieldIndex, prop);
    } else {
        var isUnsigned = false;
        switch (field.type) {
            case "double":
            case "float":gen
                ("m%s=Number(d%s)", prop, prop);
                break;
            case "uint32":
            case "fixed32": gen
                ("m%s=d%s>>>0", prop, prop);
                break;
            case "int32":
            case "sint32":
            case "sfixed32": gen
                ("m%s=d%s|0", prop, prop);
                break;
            case "uint64":
                isUnsigned = true;
                // eslint-disable-line no-fallthrough
            case "int64":
            case "sint64":
            case "fixed64":
            case "sfixed64": gen
                ("if(util.Long)")
                    ("(m%s=util.Long.fromValue(d%s)).unsigned=%j", prop, prop, isUnsigned)
                ("else if(typeof d%s===\"string\")", prop)
                    ("m%s=parseInt(d%s,10)", prop, prop)
                ("else if(typeof d%s===\"number\")", prop)
                    ("m%s=d%s", prop, prop)
                ("else if(typeof d%s===\"object\")", prop)
                    ("m%s=new util.LongBits(d%s.low>>>0,d%s.high>>>0).toNumber(%s)", prop, prop, prop, isUnsigned ? "true" : "");
                break;
            case "bytes": gen
                ("if(typeof d%s===\"string\")", prop)
                    ("util.base64.decode(d%s,m%s=util.newBuffer(util.base64.length(d%s)),0)", prop, prop, prop)
                ("else if(d%s.length)", prop)
                    ("m%s=d%s", prop, prop);
                break;
            case "string": gen
                ("m%s=String(d%s)", prop, prop);
                break;
            case "bool": gen
                ("m%s=Boolean(d%s)", prop, prop);
                break;
            /* default: gen
                ("m%s=d%s", prop, prop);
                break; */
        }
    }
    return gen;
    /* eslint-enable no-unexpected-multiline, block-scoped-var, no-redeclare */
}
Generates a partial value fromObject conveter.
@param {Codegen} gen Codegen instance
@param {Field} field Reflected field
@param {number} fieldIndex Field index
@param {string} prop Property reference
@returns {Codegen} Codegen instance
@ignore